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 A122151 Indices n such that A122150[n] is a prime. 3
 3, 4, 13, 60, 66, 75, 175 (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,...}. Primes in A122150[n] are listed in A122152[n] = {5,19,327235662833,...}. LINKS FORMULA A122150[ a(n) ] = A122152[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, A122152, A122153. Sequence in context: A243764 A201821 A001056 * A294384 A216868 A082732 Adjacent sequences:  A122148 A122149 A122150 * A122152 A122153 A122154 KEYWORD nonn AUTHOR Alexander Adamchuk, Aug 22 2006 STATUS approved

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Last modified August 22 16:17 EDT 2019. Contains 326178 sequences. (Running on oeis4.)