OFFSET
1,1
COMMENTS
Known terms are divisible by 4^m, m >= 1.
Most, but not all terms are evenly divisible by a preceding term. a(1) = 12, a(2) = 20, a(11) = 88, and a(14) = 112 are examples of terms not divisible by an earlier term.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Max Alekseyev, PARI scripts for various problems (see invphi.gp there).
EXAMPLE
PROG
(PARI) signa(n) = {my(f = factor(n)); vecsort(f[, 2]); }
isok(n) = {my(vinv = invphi(n), vinvs = vector(#vinv, k, signa(vinv[k]))); return (#vinvs != #Set(vinvs)); }
lista(nn) = {for (n=1, nn, if (istotient(n) && isok(n), print1(n, ", ")); ); } \\ Michel Marcus, Apr 08 2018
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Torlach Rush, Apr 04 2018
EXTENSIONS
More terms from Michel Marcus, Apr 09 2018
STATUS
approved