A171600 - OEIS

%I #10 Jul 13 2016 18:10:27

%S 2,3,5,11,13,17,19,23,31,37,43,47,83,97,107,199,293,337,467,523,631,

%T 643,877,907,937,953,1097,1181,1453,1511,1753,2081,2437,3011,3407,

%U 3797,4241,4273,4339,4987,5023,5347,5531,6221,6581,6703,7331,7417,7547,8167,9001

%N Primes of the form floor(T/8) where T is a triangular number.

%C 11, 13, 17, 19, 23 together with primes of the form 16n^2 + 9n + 1, 16n^2 + 11n + 1, 16n^2 + 13n + 2, 16n^2 + 15n + 3, 16n^2 + 17n + 4, 16n^2 + 19n + 5, 16n^2 + 21n + 6, or 16n^2 + 23n + 8. - _Charles R Greathouse IV_, Apr 13 2012

%H Harvey P. Dale, <a href="/A171600/b171600.txt">Table of n, a(n) for n = 1..1000</a>

%e Floor(21/8)=2, floor(28/8)=3, floor(45/8)=5,..

%t f[n_]:=n*(n+1)/2;lst={};Do[If[PrimeQ[p=Floor[f[n]/8]],AppendTo[lst,p]],{n,7!}];lst

%t Select[Floor[#/8]&/@Accumulate[Range[500]],PrimeQ] (* _Harvey P. Dale_, Jul 13 2016 *)

%Y Cf. A000217, A171574, A171595

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Dec 12 2009