

A330826


Numbers of the form 2^((2^n)+1)*F_n, where F_n is a Fermat prime, A019434.


2




OFFSET

1,1


COMMENTS

Also numbers with powerspectral basis {F_n^2, (F_n1)^2}.
The first factor of a(n) is 2^A000051(n). The first element of the powerspectral basis of a(n) is A001146, and the second element is A330828.


LINKS

Table of n, a(n) for n=1..5.


FORMULA

a(n) =2^A000051(n)*A019434(n).


EXAMPLE

a(2) = 2^(2+1)*5 = 40, and the spectral basis of 40 is {25,16}, consisting of primes and powers.


MAPLE

F := n > 2^(2^n)+1;
a := proc(n) if isprime(F(n)) then return 2^((2^n)+1)*F(n) fi; end;


CROSSREFS

Cf. A001146, A000215, A019434, A000051, A330828.
Sequence in context: A180093 A137389 A228203 * A222806 A251429 A114072
Adjacent sequences: A330823 A330824 A330825 * A330827 A330828 A330829


KEYWORD

nonn,hard,more


AUTHOR

Walter Kehowski, Jan 06 2020


STATUS

approved



