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 A074285 Sum of the divisors of n-th triangular number. 18
 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 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

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Last modified June 9 23:28 EDT 2023. Contains 363183 sequences. (Running on oeis4.)