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A274915
Powers of odd non-Fermat primes.
1
1, 7, 11, 13, 19, 23, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 263, 269, 271, 277, 281, 283, 293, 307, 311
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
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
EXTENSIONS
Edited, new name, and corrected by Robert Israel, Sep 15 2017
STATUS
approved