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A074285 Sum of the divisors of n-th triangular number. 10
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 (list; graph; refs; listen; history; text; internal format)
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

EXAMPLE

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

MATHEMATICA

t[n_]:=n*(n+1)/2; f[n_]:=Plus@@Divisors[t[n]]; lst={}; Do[AppendTo[lst, f[n]], {n, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, Oct 08 2009 *)

PROG

(PARI) vector(66, n, sumdiv(n*(n+1)\2, d, d)) \\ Joerg Arndt, Nov 29 2014

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

CROSSREFS

Cf. A000203, A000217.

Sequence in context: A111371 A078514 A230628 * A057311 A063679 A075867

Adjacent sequences:  A074282 A074283 A074284 * A074286 A074287 A074288

KEYWORD

nonn

AUTHOR

Shyam Sunder Gupta, Sep 21 2002

STATUS

approved

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Last modified February 17 16:14 EST 2018. Contains 299296 sequences. (Running on oeis4.)