OFFSET
1,2
COMMENTS
sigma(10) = 18 is congruent to 2 = -10 mod 4 and phi(10) = 4; so 10 is a term of the sequence.
If p = 5*2^k-1 is a prime, as it happens for k = 2, 4, 8, 10, 12, 14,... (A001770), then n = 2^k*p is in the sequence, since n+sigma(n) = 6*phi(n). - Giovanni Resta, Jan 27 2014
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..59 (terms < 10^11)
MATHEMATICA
t = {1}; For[i = 1, i <= 10^6, i++; If[Mod[DivisorSigma[1, i] + i, EulerPhi[i]] == 0, AppendTo[t, i]]]; t
PROG
(PARI) isok(n) = !((sigma(n) + n) % eulerphi(n)); \\ Michel Marcus, Jan 27 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Jan 27 2014
EXTENSIONS
More terms from Michel Marcus, Jan 27 2014
STATUS
approved