OFFSET
1,2
COMMENTS
n is in the sequence if n = p^m where p is in A138889 and m >= 0. - Robert Israel, Sep 15 2017
The difference between two divisors of n is never a power of 2. The first number with this property that is not in the sequence is 91. - Robert Israel, Sep 15 2017
Subsequence of A061345.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
A277994(a(n)) = 0.
EXAMPLE
49 is in this sequence because 49 = 7^2 and 7 is not a Fermat prime.
MAPLE
N:= 500: # to get all terms <= N
P:= select(isprime, {seq(i, i=7..N, 2)}) minus {seq(2^i+1, i=1..ilog2(N))}:
sort(convert(map(p -> seq(p^k, k=0..floor(log[p](N))), P), list)); # Robert Israel, Sep 15 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Nov 11 2016
EXTENSIONS
Edited, new name, and corrected by Robert Israel, Sep 15 2017
STATUS
approved