id:A086256 - OEIS Search Results

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Number of base-2 Fermat pseudoprimes that divide 2^n-1.

+0
1

0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 2, 1, 4, 1, 2, 1, 1, 0, 13, 4, 5, 0, 2, 2, 1, 1, 13, 1, 1, 4, 7, 1, 11, 4, 14, 9, 4, 4, 28, 0, 12, 11, 12, 4, 2, 5, 28, 4, 26, 1, 63, 0, 1, 5, 12, 1, 29, 1, 12, 2, 44, 4, 101, 4, 11, 27, 12, 1, 26, 4, 15, 4, 11, 1, 75, 1, 11, 14, 36, 0, 40, 11 (list; graph; listen)

	OFFSET	`1,20`
	COMMENT	`A base-2 Fermat pseudoprime is a composite number x such that 2^x = 2 mod x.`
	LINKS	`Eric Weisstein's World of Mathematics, Pseudoprime`
	FORMULA	`a(n) = Sum{d\|n} A086249(d), the Mobius transform of A086249.`
	MATHEMATICA	`Table[d=Divisors[2^n-1]; cnt=0; Do[m=d[[i]]; If[ !PrimeQ[m]&&PowerMod[2, m, m]==2, cnt++ ], {i, Length[d]}]; cnt, {n, 100}]`
	CROSSREFS	`Cf. A001567 (base-2 pseudoprimes), A086249.` `Sequence in context: A140168 A059119 A127772 this_sequence A057550 A059150 A133186` `Adjacent sequences: A086253 A086254 A086255 this_sequence A086257 A086258 A086259`
	KEYWORD	`hard,nonn`
	AUTHOR	`T. D. Noe (noe(AT)sspectra.com), Jul 14 2003`

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Last modified July 26 23:19 EDT 2008. Contains 142293 sequences.

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