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

1,2

Comments

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

Links

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

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

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A000203, A000217, A330322.

Sequence in context: A078514 A324519 A230628 * A301252 A057311 A063679

Adjacent sequences: A074282 A074283 A074284 * A074286 A074287 A074288

Keyword

nonn

Author

Shyam Sunder Gupta, Sep 21 2002

Status

approved