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A103478
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Positive integers k for which 1 + 5*2^(k+2) divides the Fermat number 1 + 2^2^k.
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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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On Keller's linked page, to find the terms, you run through the tables and find all rows with k = 5 and with n exactly 2 greater than m, then that m belongs to this sequence. - Jeppe Stig Nielsen, Dec 04 2018
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LINKS
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EXAMPLE
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a(1)=5 because 5 is the smallest positive integer k for which 1 + 5*2^(k+2) divides the Fermat number 1 + 2^2^k.
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MATHEMATICA
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Select[Range[1, 2000], Mod[1 + PowerMod[2, 2^#, 1 + 5*2^(# + 2)], 1 + 5*2^(# + 2)] == 0 &] (* Julien Kluge, Jul 08 2016 *)
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PROG
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(PARI) isok(n) = Mod(2, 1+5*2^(n+2))^(2^n) + 1 == 0; \\ Michel Marcus, Apr 29 2016
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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Serhat Sevki Dincer (mesti_mudam(AT)yahoo.com), Feb 07 2005
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STATUS
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approved
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