A330828 The squares of the Fermat primes, A019434(n)^2.

9, 25, 289, 66049, 4295098369

Offset

1,1

Comments

Also the first element of the power-spectral basis of A330826. The second element of the power-spectral basis of A330826 is A001146(n+1), n=0..4.

Links

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

Formula

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

Example

a(1) = 3^2 = 9. The spectral basis of A330826(1) = 12 is {9,4}, consisting of primes and powers.

Maple

F := n -> 2^(2^n) + 1;
a := proc(n) if isprime(F(n)) then return F(n)^2 fi; end;
seq(a(n), n=0..4);

Mathematica

(2^2^Select[Range[0, 5], PrimeQ[2^(2^#)+1] &]+1)^2 (* Stefano Spezia, May 01 2025 *)

Crossrefs

Cf. A000215, A001146, A019434, A330829.

Sequence in context: A227891 A193065 A278911 * A201807 A228465 A048056

Adjacent sequences: A330825 A330826 A330827 * A330829 A330830 A330831

Keyword

nonn,hard,more

Author

Walter Kehowski, Jan 06 2020

Status

approved