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A115907 Numbers n such that sigma(n) plus the n-th prime is a triangular number. 2
1, 2, 9, 13, 21, 80, 112, 129, 147, 225, 308, 349, 1063, 1282, 1300, 1635, 1880, 2686, 2956, 3517, 3759, 3907, 4058, 5025, 5196, 6742, 7606, 7708, 9244, 10154, 10596, 11259, 11719, 12687, 13167, 13599, 14081, 14624, 15937, 16437, 16766, 18289 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

EXAMPLE

sigma(1880)+p(1880)=20503=T(202).

MATHEMATICA

Select[Range[25000], IntegerQ[(Sqrt[8(DivisorSigma[1, #]+Prime[#])+ 1]-1)/2]&] (* From Harvey P. Dale, June 07 2011 *)

CROSSREFS

Cf. A115882, A115908.

Sequence in context: A044904 A138946 A037385 * A063634 A178688 A163735

Adjacent sequences:  A115904 A115905 A115906 * A115908 A115909 A115910

KEYWORD

nonn

AUTHOR

Giovanni Resta (g.resta(AT)iit.cnr.it), Feb 06 2006

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Last modified February 14 16:22 EST 2012. Contains 205635 sequences.