This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A357219 #17 Oct 04 2022 13:53:59 %S A357219 13,89,151,433,701,859,1429,1889,2699,4003,4751,11173,12401,18719, %T A357219 19501,27259,33151,36313,38501,39619,49139,56951,75853,80599,83843, %U A357219 104651,129793,135979,146609,188189,205759,226799,246049,318001,367651,385001,388519,431983,454579 %N A357219 Primes of the form T(p) - 2 where T(p) is the triangular number (A000217) with prime index p in A357218. %D A357219 David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, Penguin Books, London, England, 1997, entry 496, page 142. %H A357219 Robert Israel, <a href="/A357219/b357219.txt">Table of n, a(n) for n = 1..10000</a> %F A357219 a(n) = A000217(A357218(n))-2. %p A357219 f:= n -> n*(n+1)/2-2: %p A357219 select(isprime, map(f, [seq(ithprime(i),i=1..200)])); # _Robert Israel_, Sep 20 2022 %t A357219 Select[(#*(# + 1)/2 - 2) & /@ Prime[Range[165]], PrimeQ] (* _Amiram Eldar_, Sep 18 2022 *) %o A357219 (PARI) isok(p) = my(q); isprime(p) && ispolygonal(p+2, 3, &q) && isprime(q); \\ _Michel Marcus_, Sep 19 2022 %Y A357219 Cf. A000217, A357218. %Y A357219 Subsequence of A124199. %K A357219 nonn %O A357219 1,1 %A A357219 _Bernard Schott_, Sep 18 2022 %E A357219 More terms from _David A. Corneth_, Sep 18 2022