A122152 - OEIS

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A122152

Primes in A122150[n] = Numerator[ Sum[ (-1)^(k+1) * 1/2^Prime[k], {k,1,n} ] ].

5, 19, 327235662833, 578175370366880553282134492422436321419543414585625120508329411643068012549226892303, 39731908913255031966162449696446781074231732174358868548789339497630379824042353480418749055951 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,1`
	COMMENTS	`A122150[n] = Numerator[ Sum[ (-1)^(k+1) * 1/2^Prime[k], {k,1,n} ] ] begins {1,1,5,19,305,1219,19505,78019,1248305,79891519,319566077,20452228927,327235662833,...}. Indices of primes in A122150[n] are listed in A122151[n] = {3,4,13,60,66,75,175,...}.`
	LINKS	`Table of n, a(n) for n=1..5.`
	FORMULA	`a(n) = A122150[ A122151[n] ].`
	MATHEMATICA	`Do[f=Numerator[Sum[(-1)^(k+1)*1/2^Prime[k], {k, 1, n}]]; If[PrimeQ[f], Print[{n, f}]], {n, 1, 1000}]`
	CROSSREFS	`Cf. A122150, A122151, A122153.` `Sequence in context: A270486 A278562 A013531 * A104314 A302662 A261545` `Adjacent sequences: A122149 A122150 A122151 * A122153 A122154 A122155`
	KEYWORD	`nonn`
	AUTHOR	`Alexander Adamchuk, Aug 22 2006`
	STATUS	`approved`

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Last modified April 16 05:26 EDT 2021. Contains 343030 sequences. (Running on oeis4.)