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 A330826 Numbers of the form 2^((2^n)+1)*F_n, where F_n is a Fermat prime, A019434. 2
 12, 40, 544, 131584, 8590065664 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers with power-spectral basis {F_n^2, (F_n-1)^2}. The first factor of a(n) is 2^A000051(n). The first element of the power-spectral basis of a(n) is A001146, and the second element is A330828. LINKS 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

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Last modified February 8 11:37 EST 2023. Contains 360138 sequences. (Running on oeis4.)