A171938 Record values in A138753 (a "prime" variation of the Collatz (3n+1) problem).

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

Offset: 1

Author

M. F. Hasler, Apr 01 2008

Keywords

• nonn
• hard
• more

Crossrefs

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

Programs

Mathematica

A138754[n_]:=A138754[n]=With[{p=Prime[n]},PrimePi[NextPrime[If[Mod[p,3]==2,p/2,2p]]]];
A138753[n_]:=Length[NestWhileList[A138754,n,UnsameQ,{1,4}]]-1;
A171938list[upto_]:=Module[{v,r=0},Table[If[(v=A138753[n])>r,r=v,Nothing],{n,upto}]];
A171938list[500] (* Paolo Xausa, Jul 29 2023 *)

PARI

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

Formula

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

A171938 = { A138753(m) | A138753(k) < A138753(m) for all k

Extensions

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

a(15)-a(19) from Paolo Xausa, Jul 29 2023

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