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 A122260 #14 Feb 16 2025 08:33:02
%S A122260 1,2,3,4,5,6,7,8,9,10,12,13,14,15,16,17,18,19,20,21,24,25,26,27,28,30,
%T A122260 32,34,35,36,37,38,39,40,42,45,48,49,50,51,52,54,56,57,60,63,64,65,68,
%U A122260 70,72,73,74,75,76,78,80,81,84,85,90,91,95,96,97,98,100,102,104,105,108
%N A122260 Multiplicative closure of Pierpont primes.
%C A122260 If u and v are terms then also u*v is a term; A005109 is the generating subsequence;
%C A122260 A122261(a(n)) = 1;
%C A122260 A122254 is a subsequence: a(n) = A122254(n) = A048737(n) for n < 22.
%H A122260 Ivan Neretin, <a href="/A122260/b122260.txt">Table of n, a(n) for n = 1..10000</a>
%H A122260 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PierpontPrime.html">Pierpont Prime</a>.
%F A122260 Sum_{n>=1} 1/a(n) = Product_{p in A005109} p/(p-1) = 5.80109266072985445612... - _Amiram Eldar_, Sep 27 2020
%e A122260 15 = 3 * 5 is a term since both 3 and 5 are Pierpont primes.
%t A122260 mx = 108; Select[Range@mx, Complement[FactorInteger[#][[All, 1]], Select[Prime@Range@mx, Max[FactorInteger[# - 1][[All, 1]]] < 5 &], {1}] == {} &] (* _Ivan Neretin_, Aug 13 2015 *)
%o A122260 (PARI) sm3(n)=n>>=valuation(n,2);n==3^valuation(n,3)
%o A122260 is(n)=my(f=factor(n)[,1]);for(i=1,#f,if(!sm3(f[i]),return(0)));1 \\ _Charles R Greathouse IV_, Feb 21 2013
%Y A122260 Cf. A005109, A048737, A122254, A122261.
%K A122260 nonn,easy
%O A122260 1,2
%A A122260 _Reinhard Zumkeller_, Aug 29 2006