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A152989
Sum of proper divisors minus the number of proper divisors of triangular number A000217(n).
2
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
1,3
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
KEYWORD
nonn
AUTHOR
Omar E. Pol, Dec 20 2008
STATUS
approved