A357219 Primes of the form T(p) - 2 where T(p) is the triangular number (A000217) with prime index p in A357218.

13, 89, 151, 433, 701, 859, 1429, 1889, 2699, 4003, 4751, 11173, 12401, 18719, 19501, 27259, 33151, 36313, 38501, 39619, 49139, 56951, 75853, 80599, 83843, 104651, 129793, 135979, 146609, 188189, 205759, 226799, 246049, 318001, 367651, 385001, 388519, 431983, 454579

Offset: 1

Author

Bernard Schott, Sep 18 2022

Keywords

• nonn

References

• David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, Penguin Books, London, England, 1997, entry 496, page 142.

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000217, A357218.

Subsequence of A124199.

Programs

Maple

f:= n -> n*(n+1)/2-2:
select(isprime, map(f, [seq(ithprime(i),i=1..200)])); # Robert Israel, Sep 20 2022

Mathematica

Select[(#*(# + 1)/2 - 2) & /@ Prime[Range[165]], PrimeQ] (* Amiram Eldar, Sep 18 2022 *)

PARI

isok(p) = my(q); isprime(p) && ispolygonal(p+2, 3, &q) && isprime(q); \\ Michel Marcus, Sep 19 2022

Formula

a(n) = A000217(A357218(n))-2.

Extensions

More terms from David A. Corneth, Sep 18 2022