A074285 Sum of the divisors of n-th triangular number.

1, 4, 12, 18, 24, 32, 56, 91, 78, 72, 144, 168, 112, 192, 360, 270, 234, 260, 360, 576, 384, 288, 672, 868, 434, 560, 960, 720, 720, 768, 992, 1488, 864, 864, 1872, 1482, 760, 1120, 2352, 1764, 1344, 1408, 1584, 2808, 1872, 1152, 2880, 3420, 1767, 2232

Offset: 1

Author

Shyam Sunder Gupta, Sep 21 2002

Keywords

• nonn

Comments

By definition a(n) is also the sum of the divisors of n-th generalized hexagonal number. - Omar E. Pol, Nov 24 2015

Examples

			a(4)=18 because the sum of divisors of the 4th triangular number (i.e., 10) is 1 + 2 + 5 + 10 = 18.
		

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000203, A000217, A330322.

Programs

Mathematica

Table[DivisorSigma[1, n*(n + 1)/2], {n, 1, 100}] (* Vaclav Kotesovec, Aug 18 2021 *)

PARI

a(n) = sigma(n*(n+1)/2); \\ Altug Alkan, Nov 24 2015

Formula

a(n) = A000203(A000217(n)). - Omar E. Pol, Nov 24 2015

Sum_{k=1..n} a(k) ~ n^3/3. - Vaclav Kotesovec, Aug 18 2021