OFFSET
1,1
LINKS
Jud McCranie, Table of n, a(n) for n = 1..316 (First 235 terms from Donovan Johnson)
EXAMPLE
If n = 3*2^s, cototient(n) = 3*2^s-2*2^(s-1)=2^(s+1); if n = 7*2^s, cototient(n) = (7-6)*2^(s-1) = 2^(s+2). If cototient(x) = 32768, then arguments are 3*16384, 7*8192, 31*2048, 127*512, 8191*8 and 65536. If n = (2^w)*q, where q is a Mersenne prime, then phi(n) = (q-1)*2^(w-1) and the cototient(n) = 2^(w-1)*(2q-q+1) = 2^(w-1)*(q+1) = 2^(w-1+s).
MATHEMATICA
Select[Range[4, 15000], And[CompositeQ@ #, IntegerQ@ Log2[# - EulerPhi@ #]] &] (* Michael De Vlieger, Mar 05 2017 *)
PROG
(PARI) isok(n) = !isprime(n) && (c = (n - eulerphi(n))) && ((c == 2) || (ispower(c, , &x) && (x == 2))); \\ Michel Marcus, Dec 17 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jan 18 2000
STATUS
approved