A274472 Number of iterations of the Collatz recursion required to reach a prime number.

2, 0, 0, 1, 0, 1, 0, 2, 3, 1, 0, 2, 0, 1, 2, 3, 0, 4, 0, 2, 6, 1, 0, 3, 3, 1, 2, 2, 0, 3, 0, 4, 6, 1, 2, 5, 0, 1, 2, 3, 0, 7, 0, 2, 4, 1, 0, 4, 3, 4, 6, 2, 0, 3, 2, 3, 3, 1, 0, 4, 0, 1, 17, 5, 6, 7, 0, 2, 5, 3, 0, 6, 0, 1, 2, 2, 4, 3, 0, 4, 3, 1, 0, 8, 8, 1, 2

Offset

1,1

Comments

If n is prime then a(n)=0. If n is composite then a(n)=A280929(n). - Dmitry Kamenetsky, Jan 11 2017

Links

Seiichi Manyama, Table of n, a(n) for n = 1..10000

Index entries for sequences related to 3x+1 (or Collatz) problem

Mathematica

Table[Length@ NestWhileList[If[EvenQ@ #, #/2, 3 # + 1] &, n, ! PrimeQ@ # &] - 1, {n, 120}] (* Michael De Vlieger, Jun 26 2016 *)

Prog

(PARI) a(n) = my(i=0, k=n); while(!ispseudoprime(k), if(k%2==0, k=k/2, k=3*k+1); i++); i
for(n=1, 87, print1(a(n), ", ")) \\ Felix Fröhlich, Jun 24 2016

Crossrefs

Cf. A000040, A006877, A280929.

Sequence in context: A256572 A025463 A327686 * A283669 A220945 A089224

Adjacent sequences: A274469 A274470 A274471 * A274473 A274474 A274475

Keyword

nonn

Author

Matthew Campbell, Jun 24 2016

Extensions

More terms from Felix Fröhlich, Jun 24 2016

Status

approved