A263457 Integers m such that A006218(m) is triangular.

1, 2, 5, 15, 20, 26, 55, 68, 92, 108, 150, 156, 336, 346, 364, 423, 563, 586, 682, 798, 866, 951, 1194, 1734, 1888, 2790, 3102, 3150, 3506, 4210, 4611, 5820, 6766, 6943, 7665, 7701, 7888, 8734, 8772, 9410, 10114, 10839, 10969, 11014, 11453, 11630, 11947, 12357

Offset

1,2

Links

Chai Wah Wu, Table of n, a(n) for n = 1..1000

Example

If A027750 is displayed as a regular triangle:
   1;      <--1
   1,  2;       <--2
   1,  3;  1,
   2,  4;  1,  5;       <--5
   1,  2,  3,  6;  1,
   7;  1,  2,  4,  8;  1,
   3,  9;  1,  2,  5, 10;  1,
  11;  1,  2,  3,  4,  6, 12;  1,
  13;  1,  2,  7, 14;  1,  3,  5, 15;      <-- 15

Prog

(PARI) lista(nn) = {s = 0; for (n=1, nn, s += numdiv(n); if (ispolygonal(s, 3), print1(n, ", ")); ); }
(Python)
from sympy import integer_nthroot, divisor_count
A263457_list, s = [], 0
for n in range(1, 10**4):
    s += divisor_count(n)
    if integer_nthroot(8*s+1, 2)[1]:
        A263457_list.append(n) # Chai Wah Wu, Oct 09 2021

Crossrefs

Cf. A000005, A006218, A027750, A175345.

Sequence in context: A058221 A349734 A146122 * A146121 A066883 A146120

Adjacent sequences: A263454 A263455 A263456 * A263458 A263459 A263460

Keyword

nonn

Author

Michel Marcus, Oct 19 2015

Status

approved