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 A384512 #10 Jun 15 2025 20:03:51 %S A384512 2,3,13,17,37,41,61,613,829,1861,2269,7333,35149,1008229,909889549, %T A384512 1423665384101,10341624100573,440171836495742615578609, %U A384512 471206109194322691633610979351605854911441181,4466501842784976704198682186832272945270823914876207595593007001786562643495541 %N A384512 Record terms in A384698. %F A384512 a(n) mod 4 = 1, n > 2. %e A384512 41 is a term because iterating the map on 12 results in a prime in 3 steps: 12 -> 2*12+1=25 -> 25-5=20 -> 2*20+1=41 and 41 is a record prime for starting integers <= 12. %o A384512 (Python) %o A384512 from sympy import isprime, primefactors; rec = 1 %o A384512 for n in range (2, 158163): %o A384512 while not isprime(n): n = n - min(primefactors(n)) if n%2 else 2*n + 1 %o A384512 if n > rec: rec = n; print(n, end = ', ') %Y A384512 Cf. A020639 (lpf), A383777, A384698. %K A384512 nonn %O A384512 1,1 %A A384512 _Ya-Ping Lu_, May 31 2025