OFFSET
1,2
COMMENTS
This sequence is the complement of A303746.
LINKS
Max Alekseyev, PARI scripts for various problems (for invphi pari script).
K. B. Stolarski and S. Greenbaum, A Ratio Associated with phi(x) = n, The Fibonacci Quarterly, Volume 23, Number 3, August 1985, pp. 265-269.
EXAMPLE
1 is a term because there is no prime that divides the solutions of phi(x) = 1 (1 and 2).
2 is a term because there is no prime that divides the solutions of phi(x) = 2 (3, 4, and 6).
10 is not a term because 11 divides solutions of phi(x) = 10 (11 and 22) yielding 1 and 2 the solutions of phi(x) = 1.
PROG
(PARI) isok(n) = {if (istotient(n), v = invphi(n); g = gcd(v); if (g == 1, return (1)); f = factor(g); for (k=1, #f~, vv = v/f[k, 1]; nt = eulerphi(vv[1]); if (vv == invphi(nt), return(0)); ); return (1); ); } \\ Michel Marcus, Jul 25 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Torlach Rush, Jun 21 2018
STATUS
approved