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 A138756 #10 Aug 02 2023 14:11:42
%S A138756 1,2,3,8,11,17,18,27,42,72,125,219,221,401,515,556,754,841,1146
%N A138756 Indices of record values in A138753 (a "prime" variation of the Collatz (3n+1) problem).
%C A138756 "Indices of ..." is equivalent to "starting values for ..."
%F A138756 a(n) = min { k | A138753(k) = A171938(n) }
%F A138756 Equals { m | A138753(k) < A138753(m) for all k<m }
%t A138756 A138754[n_]:=A138754[n]=With[{p=Prime[n]},PrimePi[NextPrime[If[Mod[p,3]==2,p/2,2p]]]];
%t A138756 A138753[n_]:=Length[NestWhileList[A138754,n,UnsameQ,{1,4}]]-1;
%t A138756 A138756list[upto_]:=Module[{v,r=0},Table[If[(v=A138753[n])>r,r=v;n,Nothing],{n,upto}]];
%t A138756 A138756list[500] (* _Paolo Xausa_, Jul 30 2023 *)
%o A138756 (PARI) m=0; for( i=1,#A138753, A138753[i] > m || next; m=A138753[i]; print1(i", "))
%Y A138756 Cf. A124123, A138750-A138754, A171938, A006877 (analog for Collatz problem).
%K A138756 nonn,hard,more
%O A138756 1,2
%A A138756 _M. F. Hasler_, Apr 01 2008
%E A138756 a(15)-a(19) from _Paolo Xausa_, Jul 30 2023