A166119 - OEIS

%I #8 Sep 18 2024 14:17:50

%S 3,10,23,25,213,270,455,688,1060,1953,2233,2915,3468,3838,4718,4945,

%T 8645,10230,11638,12308,13090,15428,16250,19295,23095,27778,29435,

%U 32230,33488,43053,50830,71668,83485,86460,89365,96330,104610,106600,127823

%N a(n) = A165966(n)/12.

%C The only known primes in the sequence are 3, 23.

%F a(n) = (A086816(n) + 1)/6. - _Alois P. Heinz_, Sep 18 2024

%o (PARI) lista(nn) = {for (n = 1, nn, trg = n*(n+1)/2; if (!(trg % 2) && isprime(trg/2-1) && isprime(trg/2+1), print1(trg/12, ", ")););} \\ _Michel Marcus_, Oct 16 2013

%Y Cf. A000217, A001359, A086816, A105174, A111163, A165966.

%K nonn

%O 1,1

%A _Zak Seidov_, Oct 07 2009