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 A115883 The n-th prime minus n gives a triangular number. 4
 1, 2, 4, 5, 7, 13, 34, 37, 46, 62, 104, 111, 210, 259, 274, 296, 306, 439, 488, 502, 513, 751, 763, 817, 969, 998, 1132, 1231, 1405, 1586, 1849, 1982, 2107, 2488, 2578, 2695, 2732, 2752, 2989, 3008, 3079, 3322, 3958, 4201, 4628, 5035, 5594, 5722, 5929 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Harvey P. Dale and T. D. Noe, Table of n, a(n) for n = 1..1000 (first 500 terms from Harvey P. Dale) EXAMPLE prime(13)-13 = 41-13 = 28 = T(7). MATHEMATICA Flatten[Position[Table[Prime[n]-n, {n, 6000}], _?(IntegerQ[(Sqrt[ 8#+1]- 1)/2]&)]] (* Harvey P. Dale, Oct 08 2012 *) pntQ[{a_, b_}]:=OddQ[Sqrt[8(a-b)+1]]; Module[{nn=6000}, Select[Thread[ {Prime[ Range[nn]], Range[nn]}], pntQ]][[All, 2]] (* Harvey P. Dale, Dec 20 2019 *) PROG (PARI) isok(n) = ispolygonal(prime(n) - n, 3); \\ Michel Marcus, Jan 25 2014 CROSSREFS Cf. A064370, A115882, A115887. Sequence in context: A115008 A275368 A332296 * A063508 A101724 A123210 Adjacent sequences:  A115880 A115881 A115882 * A115884 A115885 A115886 KEYWORD nonn AUTHOR Giovanni Resta, Feb 06 2006 STATUS approved

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Last modified November 29 05:25 EST 2020. Contains 338756 sequences. (Running on oeis4.)