A357219 - OEIS

%I #17 Oct 04 2022 13:53:59

%S 13,89,151,433,701,859,1429,1889,2699,4003,4751,11173,12401,18719,

%T 19501,27259,33151,36313,38501,39619,49139,56951,75853,80599,83843,

%U 104651,129793,135979,146609,188189,205759,226799,246049,318001,367651,385001,388519,431983,454579

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

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

%H Robert Israel, <a href="/A357219/b357219.txt">Table of n, a(n) for n = 1..10000</a>

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

%p f:= n -> n*(n+1)/2-2:

%p select(isprime, map(f, [seq(ithprime(i),i=1..200)])); # _Robert Israel_, Sep 20 2022

%t Select[(#*(# + 1)/2 - 2) & /@ Prime[Range[165]], PrimeQ] (* _Amiram Eldar_, Sep 18 2022 *)

%o (PARI) isok(p) = my(q); isprime(p) && ispolygonal(p+2, 3, &q) && isprime(q); \\ _Michel Marcus_, Sep 19 2022

%Y Cf. A000217, A357218.

%Y Subsequence of A124199.

%K nonn

%O 1,1

%A _Bernard Schott_, Sep 18 2022

%E More terms from _David A. Corneth_, Sep 18 2022