

A115883


The nth 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
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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 = 4113 = 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(ab)+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



