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 A237048 Irregular triangle read by rows: T(n,k), n >= 1, k >= 1, in which column k lists 1's interleaved with k-1 zeros, and the first element of column k is in row k(k+1)/2. 156
 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1 COMMENTS The sum of row n gives A001227(n), the number of odd divisors of n. Row n has length A003056(n) hence column k starts in row A000217(k). If n = 2^j then the only positive integer in row n is T(n,1) = 1. If n is an odd prime then the only two positive integers in row n are T(n,1) = 1 and T(n,2) = 1. The partial sums of column k give the column k of A235791. The connection with A196020 is as follow: A235791 --> A236104 --> A196020. The connection with the symmetric representation of sigma is as follows: A235791 --> A237591 --> A237593 --> A239660 --> A237270. From Hartmut F. W. Hoft, Oct 23 2014: (Start) Property: Let n = 2^m*s*t with m >= 0 and 1 <= s, t odd, and r(n) = floor(sqrt(8*n+1) - 1)/2) = A003056(n). T(n, k) = 1 precisely when k is odd and k|n, or k = 2^(m+1)*s when 1 <= s < 2^(m+1)*s <= r(n) < t. Thus each odd divisor greater than r(n) is matched by a unique even index less than or equal to r(n). For further connections with the symmetric representation of sigma see also A249223. (End) From Omar E. Pol, Jan 21 2017: (Start) Conjecture 1: alternating sum of row n gives A067742(n), the number of middle divisors of n. The sum of row n also gives the number of subparts in the symmetric representation of sigma(n), equaling A001227(n), the number of odd divisors of n. For more information see A279387. (End) From Omar E. Pol, Feb 08 2017, Feb 22 2017: (Start) Conjecture 2: Alternating sum of row n also gives the number of central subparts in the symmetric representation of sigma(n), equaling the width of the terrace at the n-th level in the main diagonal of the pyramid described in A245092. Conjecture 3: The sum of the odd-indexed terms in row n gives A082647(n): the number of odd divisors of n less than sqrt(2*n), also the number of partitions of n into an odd number of consecutive parts. Conjecture 4: The sum of the even-indexed terms in row n gives A131576(n): the number of odd divisors of n greater than sqrt(2*n), also the number of partitions of n into an even number of consecutive parts. Conjecture 5: The sum of the even-indexed terms in row n also gives the number of pairs of equidistant subparts in the symmetric representation of sigma(n). (End) Conjecture 6: T(n,k) is also the number of partitions of n into exactly k consecutive parts. - Omar E. Pol, Apr 28 2017 LINKS G. C. Greubel, Table of n, a(n) for the first 150 rows, flattened FORMULA For n >= 1 and k = 1, ..., A003056(n): if k is odd then T(n, k) = 1 if k|n, otherwise 0, and if k is even then T(n, k) = 1 if k|(n-k/2), otherwise 0. - Hartmut F. W. Hoft, Oct 23 2014 a(n) = A057427(A196020(n)) = A057427(A261699(n)). - Omar E. Pol, Nov 14 2016 A000203(n) = Sum_{k=1..A003056(n)} (-1)^(k-1) * ((Sum_{j=k*(k+1)/2..n} T(j,k))^2 - (Sum_{j=k*(k+1)/2..n} T(j-1,k))^2), assuming that T(k*(k+1)/2-1,k) = 0. - Omar E. Pol, Oct 10 2018 EXAMPLE Triangle begins (rows 1..28): 1; 1; 1,  1; 1,  0; 1,  1; 1,  0,  1; 1,  1,  0; 1,  0,  0; 1,  1,  1; 1,  0,  0,  1; 1,  1,  0,  0; 1,  0,  1,  0; 1,  1,  0,  0; 1,  0,  0,  1; 1,  1,  1,  0,  1; 1,  0,  0,  0,  0; 1,  1,  0,  0,  0; 1,  0,  1,  1,  0; 1,  1,  0,  0,  0; 1,  0,  0,  0,  1; 1,  1,  1,  0,  0,  1; 1,  0,  0,  1,  0,  0; 1,  1,  0,  0,  0,  0; 1,  0,  1,  0,  0,  0; 1,  1,  0,  0,  1,  0; 1,  0,  0,  1,  0,  0; 1,  1,  1,  0,  0,  1; 1,  0,  0,  0,  0,  0,  1; ... For n = 20 the divisors of 20 are 1, 2, 4, 5, 10, 20. There are two odd divisors: 1 and 5. On the other hand the 20th row of triangle is [1, 0, 0, 0, 1] and the row sum is 2, equaling the number of odd divisors of 20. From Hartmut F. W. Hoft, Oct 23 2014: (Start) For n = 18 the divisors are 1, 2, 3, 6, 9, 18. There are three odd divisors: 1 and 3 are in their respective columns, but 9 is accounted for in column 4 = 2^2*1 since 18 = 2^1*1*9 and 9>5, the number of columns in row 18. (End) From Omar E. Pol, Dec 17 2016: (Start) Illustration of initial terms: Row                                                         _ 1                                                         _|1| 2                                                       _|1 _| 3                                                     _|1  |1| 4                                                   _|1   _|0| 5                                                 _|1    |1 _| 6                                               _|1     _|0|1| 7                                             _|1      |1  |0| 8                                           _|1       _|0 _|0| 9                                         _|1        |1  |1 _| 10                                      _|1         _|0  |0|1| 11                                    _|1          |1   _|0|0| 12                                  _|1           _|0  |1  |0| 13                                _|1            |1    |0 _|0| 14                              _|1             _|0   _|0|1 _| 15                            _|1              |1    |1  |0|1| 16                          _|1               _|0    |0  |0|0| 17                        _|1                |1     _|0 _|0|0| 18                      _|1                 _|0    |1  |1  |0| 19                    _|1                  |1      |0  |0 _|0| 20                  _|1                   _|0     _|0  |0|1 _| 21                _|1                    |1      |1   _|0|0|1| 22              _|1                     _|0      |0  |1  |0|0| 23            _|1                      |1       _|0  |0  |0|0| 24          _|1                       _|0      |1    |0 _|0|0| 25        _|1                        |1        |0   _|0|1  |0| 26      _|1                         _|0       _|0  |1  |0 _|0| 27    _|1                          |1        |1    |0  |0|1 _| 28   |1                            |0        |0    |0  |0|0|1| ... Note that the 1's are placed exactly below the horizontal line segments. Also the above structure represents the left hand part of the front view of the pyramid described in A245092. For more information about the pyramid and the symmetric representation of sigma see A237593. (End) MAPLE r := proc(n) floor((sqrt(1+8*n)-1)/2) ; end proc: # A003056 A237048:=proc(n, k) local i; global r; if n<(k-1)*k/2 or k>r(n) then return(0); fi; if (k mod 2)=1 and (n mod k)=0 then return(1); fi; if (k mod 2)=0 and ((n-k/2) mod k) = 0 then return(1); fi; return(0); end; for n from 1 to 12 do lprint([seq(A237048(n, k), k=1..r(n))]); od; # N. J. A. Sloane, Jan 15 2021 MATHEMATICA cd[n_, k_] := If[Divisible[n, k], 1, 0] row[n_] := Floor[(Sqrt[8n+1] - 1)/2] a237048[n_, k_] := If[OddQ[k], cd[n, k], cd[n - k/2, k]] a237048[n_] := Map[a237048[n, #]&, Range[row[n]]] Flatten[Map[a237048, Range]] (* data: 24 rows of triangle *) (* Hartmut F. W. Hoft, Oct 23 2014 *) PROG (PARI) t(n, k) = if (k % 2, (n % k) == 0, ((n - k/2) % k) == 0); tabf(nn) = {for (n=1, nn, for (k=1, floor((sqrt(1+8*n)-1)/2), print1(t(n, k), ", "); ); print(); ); } \\ Michel Marcus, Sep 20 2015 (Python) from sympy import sqrt import math def T(n, k): return (n%k == 0)*1 if k%2 == 1 else (((n - k/2)%k) == 0)*1 for n in range(1, 21): print([T(n, k) for k in range(1, int(math.floor((sqrt(8*n + 1) - 1)/2)) + 1)]) # Indranil Ghosh, Apr 21 2017 CROSSREFS Cf. A000203, A285898, A001227, A003056, A057427, A067742, A082647, A131576, A196020, A236104, A235791, A237270, A237271, A237591, A237593, A239657, A245092, A249351, A261699, A262611, A262626, A279387, A279693. The MMA code here is used also in A262045. Sequence in context: A142720 A196308 A091862 * A167020 A236862 A163812 Adjacent sequences:  A237045 A237046 A237047 * A237049 A237050 A237051 KEYWORD nonn,easy,tabf AUTHOR Omar E. Pol, Mar 01 2014 STATUS approved

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Last modified April 22 15:43 EDT 2021. Contains 343177 sequences. (Running on oeis4.)