A374237 Irregular triangle read by rows where row n lists, in increasing order, the divisors of 2^n + 1.

1, 2, 1, 3, 1, 5, 1, 3, 9, 1, 17, 1, 3, 11, 33, 1, 5, 13, 65, 1, 3, 43, 129, 1, 257, 1, 3, 9, 19, 27, 57, 171, 513, 1, 5, 25, 41, 205, 1025, 1, 3, 683, 2049, 1, 17, 241, 4097, 1, 3, 2731, 8193, 1, 5, 29, 113, 145, 565, 3277, 16385, 1, 3, 9, 11, 33, 99, 331, 993, 2979, 3641, 10923, 32769

Offset: 0

Author

Paolo Xausa, Jul 02 2024

Keywords

• nonn
• tabf
• look

Examples

			Triangle begins:
   [0]  1,   2;
   [1]  1,   3;
   [2]  1,   5;
   [3]  1,   3,  9;
   [4]  1,  17;
   [5]  1,   3, 11,  33;
   [6]  1,   5, 13,  65;
   [7]  1,   3, 43, 129;
   [8]  1, 257;
   [9]  1,   3,  9,  19,  27,   57, 171, 513;
  [10]  1,   5, 25,  41, 205, 1025;
  ...
		

Links

• Paolo Xausa, Table of n, a(n) for n = 0..11484 (rows 0..135 of the triangle, flattened).
• Index entries for sequences related to divisors of numbers

Crossrefs

Subsequence of A027750.

Cf. A000051, A002586 (2nd column), A046798 (row lengths), A069060 (row products), A069061 (row sums).

Cf. A361438 (analogous for 2^n - 1).

Programs

Maple

T:= n-> sort([numtheory[divisors](2^n+1)[]])[]:
seq(T(n), n=0..15);  # Alois P. Heinz, Oct 20 2024

Mathematica

Divisors[2^Range[0, 20] + 1]