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A330826
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Numbers of the form 2^((2^n)+1)*F_n, where F_n is a Fermat prime, A019434.
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2
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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Table of n, a(n) for n=1..5.
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FORMULA
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a(n) =2^A000051(n)*A019434(n).
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EXAMPLE
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a(2) = 2^(2+1)*5 = 40, and the spectral basis of 40 is {25,16}, consisting of primes and powers.
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MAPLE
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F := n -> 2^(2^n)+1;
a := proc(n) if isprime(F(n)) then return 2^((2^n)+1)*F(n) fi; end;
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CROSSREFS
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Cf. A001146, A000215, A019434, A000051, A330828.
Sequence in context: A180093 A137389 A228203 * A222806 A251429 A114072
Adjacent sequences: A330823 A330824 A330825 * A330827 A330828 A330829
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KEYWORD
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nonn,hard,more
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AUTHOR
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Walter Kehowski, Jan 06 2020
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STATUS
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approved
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