OFFSET
1,2
COMMENTS
The sequence of positive odd integers not in this sequence begins {61, 81, 123, 139, ...}. When x(1) is any of these, the sequence x(i) enters a cycle of 931 values x(i) = x(i+931)=1163.
LINKS
Pierre CAMI, PFGW Script
PROG
(PARI) f(n) = if (n % 2, if (isprime(n), 2*n+1, 3*n+1), n/2);
isok(n) = {if (n%2, while (1, n = f(n); if (n==1, return (1)); if (n==1163, return (0)); ); ); } \\ Michel Marcus, Mar 28 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Feb 18 2018
STATUS
approved