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 A115904 Numbers n such that n+sigma(n) is a triangular number. 3
 7, 10, 66, 136, 145, 196, 198, 234, 270, 438, 495, 528, 592, 606, 855, 910, 1045, 1158, 1428, 2208, 2718, 2922, 3016, 3663, 3808, 3916, 4506, 4975, 5043, 5136, 5598, 6366, 6600, 7080, 7498, 7821, 8172, 8200, 8217, 8814, 9318, 9730, 9738 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE 234+sigma(234)=780=T(39). MATHEMATICA trnoQ[n_]:=IntegerQ[(Sqrt[1+8n]-1)/2]; Select[Range[10000], trnoQ[#+ DivisorSigma[ 1, #]]&] (* Harvey P. Dale, Apr 26 2014 *) PROG (PARI) isok(n) = ispolygonal(n + sigma(n), 3); \\ Michel Marcus, Jan 25 2014 CROSSREFS Cf. A069066, A115907, A115909. Sequence in context: A249952 A187999 A097187 * A136865 A123797 A123805 Adjacent sequences:  A115901 A115902 A115903 * A115905 A115906 A115907 KEYWORD nonn AUTHOR Giovanni Resta, Feb 06 2006 STATUS approved

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Last modified April 8 00:29 EDT 2020. Contains 333311 sequences. (Running on oeis4.)