A171938 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

FORMULA

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

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 *)

PROG

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

CROSSREFS

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

KEYWORD

nonn,hard,more

AUTHOR

M. F. Hasler, Apr 01 2008

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

STATUS

approved