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 A246278 Square array read by antidiagonals: A(1,col) = 2*col, and for row > 1, A(row,col) = A003961(A(row-1,col)). 46
 2, 4, 3, 6, 9, 5, 8, 15, 25, 7, 10, 27, 35, 49, 11, 12, 21, 125, 77, 121, 13, 14, 45, 55, 343, 143, 169, 17, 16, 33, 175, 91, 1331, 221, 289, 19, 18, 81, 65, 539, 187, 2197, 323, 361, 23, 20, 75, 625, 119, 1573, 247, 4913, 437, 529, 29, 22, 63, 245, 2401, 209, 2873, 391, 6859, 667, 841, 31 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS The array is read by antidiagonals: A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), etc. This array can be obtained by taking every second column from array A242378, starting from its column 2. Permutation of natural numbers larger than 1. The terms on row n are all divisible by n-th prime, A000040(n). Each column is strictly growing, and the terms in the same column have the same prime signature. A055396(n) gives the row number of row where n occurs, and A246277(n) gives its column number, both starting from 1. From Antti Karttunen, Jan 03 2015: (Start) A252759(n) gives their sum minus one, i.e. the Manhattan distance of n from the top left corner. If we assume here that a(1) = 1 (but which is not explicitly included because outside of the array), then A252752 gives the inverse permutation. See also A246276. (End) LINKS FORMULA A(1,col) = 2*col, and for row > 1, A(row,col) = A003961(A(row-1,col)). As a composition of other similar sequences: a(n) = A122111(A253561(n)). a(n) = A249818(A083221(n)). For all n >= 1, a(n+1) = A005940(1+A253551(n)). EXAMPLE The top left corner of the array:    2,     4,     6,     8,    10,    12,    14,    16,    18, ...    3,     9,    15,    27,    21,    45,    33,    81,    75, ...    5,    25,    35,   125,    55,   175,    65,   625,   245, ...    7,    49,    77,   343,    91,   539,   119,  2401,   847, ...   11,   121,   143,  1331,   187,  1573,   209, 14641,  1859, ...   13,   169,   221,  2197,   247,  2873,   299, 28561,  3757, ... MATHEMATICA f[p_?PrimeQ] := f[p] = Prime[PrimePi@ p + 1]; f[1] = 1; f[n_] := f[n] = Times @@ (f[First@ #]^Last@ # &) /@ FactorInteger@ n; Block[{lim = 12}, Table[#[[n - k, k]], {n, 2, lim}, {k, n - 1, 1, -1}] &@ NestList[Map[f, #] &, Table[2 k, {k, lim}], lim]] // Flatten (* Michael De Vlieger, Jan 04 2016, after Jean-François Alcover at A003961 *) PROG (Scheme) (define (A246278 n) (if (<= n 1) n (A246278bi (A002260 (- n 1)) (A004736 (- n 1))))) ;; Square array starts with offset=2, and we have also tacitly defined a(1) = 1 here. (define (A246278bi row col) (if (= 1 row) (* 2 col) (A003961 (A246278bi (- row 1) col)))) CROSSREFS First row: A005843 (the even numbers), from 2 onward. Row 2: A249734, Row 3: A249827. Column 1: A000040 (primes), Column 2: A001248 (squares of primes), Column 3: A006094 (products of two successive primes), Column 4: A030078 (cubes of primes). Transpose: A246279. Inverse permutation: A252752. One more than A246275. Cf. A005940, A242378, A246259, A000040, A002260, A004736, A003961, A055396, A083221, A122111, A114537, A246277, A246675, A246684, A249818, A252759, A253561, A253515. Sequence in context: A293054 A255127 A083221 * A246366 A271865 A075652 Adjacent sequences:  A246275 A246276 A246277 * A246279 A246280 A246281 KEYWORD nonn,tabl AUTHOR Antti Karttunen, Aug 21 2014 EXTENSIONS Starting offset of the linear sequence changed from 1 to 2, without affecting the column and row indices by Antti Karttunen, Jan 03 2015 STATUS approved

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Last modified August 24 16:59 EDT 2019. Contains 326295 sequences. (Running on oeis4.)