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A330825
Numbers of the form 2^(2^k)*F_k, where F_k is a Fermat prime, A019434.
1
6, 20, 272, 65792, 4295032832
OFFSET
1,1
COMMENTS
Also numbers with power-spectral basis {F_n,(F_n-1)^2}. The first element of the power-spectral basis of a(n) is A019434, and the second element is A001146.
FORMULA
a(n) = A001146(n-1)*A019434(n), n = 1..5. [Corrected by Georg Fischer, Dec 09 2022]
EXAMPLE
a(2) = 2^2*(2^2+1) = 20, and the spectral basis of 20 is {5,16}, consisting of primes and powers.
MAPLE
F := n -> 2^(2^n)+1;
a := proc(n) if isprime(F(n)) then return 2^(2^n)*F(n) fi; end;
[seq(a(n), n=0..4)];
CROSSREFS
KEYWORD
nonn
AUTHOR
Walter Kehowski, Jan 06 2020
STATUS
approved