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 A380312 #16 Jan 24 2025 23:20:08 %S A380312 19,29,37,67,73,101,131,167,181,197,211,241,251,257,317,389,421,463, %T A380312 479,503,523,599,643,653,691,719,739,811,827,859,887,907,919,941,983, %U A380312 1039,1061,1069,1109,1117,1217,1277,1283,1289,1307,1361,1381,1427,1429,1499 %N A380312 Primes not reaching 3 under iterations of p -> gpf(2*p-1). %C A380312 It appears that this is the primes reaching 19 under iterations of p -> gpf(2*p-1). %C A380312 Conjecture: a(n) ~ k*n log n for some constant k. Perhaps k ≈ 4.51. - _Charles R Greathouse IV_, Jan 24 2025 %e A380312 19, 37, 73 and 29 are in the sequence as they form a loop under the iteration. %o A380312 (PARI) \\ This will loop forever if it hits a loop other than 3 or 19, but if it returns the result is correct. %o A380312 gpf(n)=my(f=factor(n)[,1]); f[#f] %o A380312 is(p)=while(p>28, p=gpf(2*p-1)); p==19 \\ _Charles R Greathouse IV_, Jan 24 2025 %Y A380312 Cf. A006530, A023583. %K A380312 easy,nonn %O A380312 1,1 %A A380312 _Johannes M.V.A. Koelman_, Jan 20 2025