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

Offset: 1

Author

Omar E. Pol, Dec 20 2008

Keywords

• nonn

Links

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

Crossrefs

Cf. A000005, A000203, A000217, A001065, A032741, A152770.

Programs

Mathematica

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

PARI

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

Formula

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