%I #5 Sep 15 2024 22:04:55
%S 3,5,7,11,13,17,19,23,29,37,41,43,47,53,61,71,73,89,97,107,131,149,
%T 157,163,167,179,193,197,211,223,233,251,257,269,271,277,281,307,313,
%U 337,359,389,401,409,419,431,439,443,457,467,503,509,521,541,571,613,641,673,691
%N Prime indices of triangular numbers k such that either k + 1 or k - 2 is prime.
%D David Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, Revised edition 1987. See entry 496 at p. 155.
%e 29 is a term since it is prime and A000217(29) - 2 = 433 is prime.
%t Select[Range[700], PrimeQ[#]&&(PrimeQ[t=#(#+1)/2+1]||PrimeQ[t-3]) &]
%Y Cf. A000040 (supersequence), A000124, A000217, A034856.
%Y Complement of A376205 in A000040.
%K nonn,easy
%O 1,1
%A _Stefano Spezia_, Sep 15 2024