A376206 Prime indices of triangular numbers k such that either k + 1 or k - 2 is prime.

3, 5, 7, 11, 13, 17, 19, 23, 29, 37, 41, 43, 47, 53, 61, 71, 73, 89, 97, 107, 131, 149, 157, 163, 167, 179, 193, 197, 211, 223, 233, 251, 257, 269, 271, 277, 281, 307, 313, 337, 359, 389, 401, 409, 419, 431, 439, 443, 457, 467, 503, 509, 521, 541, 571, 613, 641, 673, 691

Offset: 1

Author

Stefano Spezia, Sep 15 2024

Keywords

• nonn
• easy

Examples

			29 is a term since it is prime and A000217(29) - 2 = 433 is prime.
		

References

• David Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, Revised edition 1987. See entry 496 at p. 155.

Crossrefs

Cf. A000040 (supersequence), A000124, A000217, A034856.

Complement of A376205 in A000040.

Programs

Mathematica

Select[Range[700], PrimeQ[#]&&(PrimeQ[t=#(#+1)/2+1]||PrimeQ[t-3]) &]