%I #11 Jul 30 2023 09:21:46

%S 1,4,5,8,21,22,24,29,60,61,72,73,97,100,184,216,239,451,469

%N Record values in A138753 (a "prime" variation of the Collatz (3n+1) problem).

%F A171938(n) = A138753(A138756(n)).

%F A171938 = { A138753(m) | A138753(k) < A138753(m) for all k<m }.

%t A138754[n_]:=A138754[n]=With[{p=Prime[n]},PrimePi[NextPrime[If[Mod[p,3]==2,p/2,2p]]]];

%t A138753[n_]:=Length[NestWhileList[A138754,n,UnsameQ,{1,4}]]-1;

%t A171938list[upto_]:=Module[{v,r=0},Table[If[(v=A138753[n])>r,r=v,Nothing],{n,upto}]];

%t A171938list[500] (* _Paolo Xausa_, Jul 29 2023 *)

%o (PARI) m=0; for( i=1,#A138753, A138753[i] > m & print1( m=A138753[i],", "))

%Y Cf. A124123, A138750-A138754, A138756, A006878 (analog for Collatz problem).

%K nonn,hard,more

%O 1,2

%A _M. F. Hasler_, Apr 01 2008

%E Originally submitted as A138755, but mislaid by Editor-in-Chief; renumbered and added to OEIS, Oct 24 2010

%E a(15)-a(19) from _Paolo Xausa_, Jul 29 2023