A273263 Irregular triangle read by rows: T(n,k) is the sum of the elements of the k-th column of the difference table of the divisors of n.

1, 2, 2, 3, 3, 3, 4, 4, 5, 5, 4, 5, 6, 6, 7, 7, 4, 6, 8, 8, 7, 9, 9, 4, 7, 10, 10, 11, 11, 4, 6, 8, 10, 12, 12, 13, 13, 4, 9, 14, 14, 11, 13, 15, 15, 5, 8, 12, 16, 16, 17, 17, 12, 11, 12, 15, 18, 18, 19, 19, -3, 4, 10, 15, 20, 20, 13, 17, 21, 21, 4, 13, 22, 22, 23, 23, -4, 3, 8, 12, 16, 20, 24, 24, 21, 25, 25

Offset

1,2

Comments

If n is prime then row n is [n, n].

It appears that the last two terms of the n-th row are [n, n], n > 1.

First differs from A274533 at a(38).

Links

Table of n, a(n) for n=1..87.

Example

Triangle begins:
   1;
   2,  2;
   3,  3;
   3,  4,  4;
   5,  5;
   4,  5,  6,  6;
   7,  7;
   4,  6,  8,  8;
   7,  9,  9;
   4,  7, 10, 10;
  11, 11;
   4,  6,  8, 10, 12, 12;
  13, 13;
   4,  9, 14, 14;
  11, 13, 15, 15;
   5,  8, 12, 16, 16;
  17, 17;
  12, 11, 12, 15, 18, 18;
  19, 19;
  -3,  4, 10, 15, 20, 20;
  13, 17, 21, 21;
   4, 13, 22, 22;
  23, 23;
  -4,  3,  8, 12, 16, 20, 24, 24;
  21, 25, 25;
   4, 15, 26, 26;
  ...
For n = 18 the divisors of 18 are 1, 2, 3, 6, 9, 18, and the difference triangle of the divisors is
   1,  2,  3,  6,  9, 18;
   1,  1,  3,  3,  9;
   0,  2,  0,  6;
   2, -2,  6;
  -4,  8;
  12;
The column sums give [12, 11, 12, 15, 18, 18] which is also the 18th row of the irregular triangle.

Mathematica

Table[Total /@ Transpose@ Map[Function[w, PadRight[w, Length@ #]], NestWhileList[Differences, #, Length@ # > 1 &]] &@ Divisors@ n, {n, 25}] // Flatten (* Michael De Vlieger, Jun 26 2016 *)

Prog

(PARI) row(n) = {my(d = divisors(n)); my(nd = #d); my(m = matrix(#d, #d)); for (j=1, nd, m[1, j] = d[j]; ); for (i=2, nd, for (j=1, nd - i +1, m[i, j] = m[i-1, j+1] - m[i-1, j]; ); ); vector(nd, j, sum(i=1, nd, m[i, j])); }
tabf(nn) = for (n=1, nn, print(row(n)); );
lista(nn) = for (n=1, nn, v = row(n); for (j=1, #v, print1(v[j], ", ")); ); \\ Michel Marcus, Jun 25 2016

Crossrefs

Row lengths give A000005. Right border gives A000027. Column 1 is A161857. Row sums give A273103.

Cf. A187202, A273102, A273135, A272210, A273136, A273261, A273262, A274533.

Sequence in context: A189717 A219519 A330393 * A274533 A163127 A077113

Adjacent sequences: A273260 A273261 A273262 * A273264 A273265 A273266

Keyword

sign,tabf

Author

Omar E. Pol, May 22 2016

Status

approved