A152989 - OEIS

A152989

Sum of proper divisors minus the number of proper divisors of triangular number A000217(n).

0, 0, 3, 5, 6, 8, 23, 47, 28, 14, 71, 83, 18, 80, 225, 127, 76, 84, 163, 351, 146, 32, 385, 551, 104, 202, 567, 307, 278, 296, 487, 941, 296, 262, 1219, 805, 54, 372, 1549, 933, 476, 498, 631, 1795, 826, 68, 1737, 2221, 534, 946, 1683, 883, 722, 1380, 2469, 2861, 740, 86, 2535

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OFFSET

1,3

LINKS

B. D. Swan, Table of n, a(n) for n=1,...,10000

FORMULA

a(n) = A001065(A000217(n)) - A032741(A000217(n)) = A152770(A000217(n)).

MATHEMATICA

DivisorSigma[1, #]-DivisorSigma[0, #]-#+1&/@Accumulate[Range[60]] (* Harvey P. Dale, May 06 2014 *)

PROG

(PARI) a(n) = sigma(n*(n+1)/2) - n*(n+1)/2 - (numdiv(n*(n+1)/2) - 1); \\ Michel Marcus, Jan 28 2014

CROSSREFS