OFFSET
1,3
COMMENTS
Denominator of Sum[ (-1)^(k+1) * 1/2^Prime[k], {k,1,n} ] equals 2^Prime[n] = A034765[n]. a(n) is prime for n = {3,4,13,60,66,75,175,...} = A122151[n]. Prime a(n) are {5,19,327235662833,...} = A122152[n]. Parity Prime Constant C = Sum[ (-1)^(k+1) * 1/2^Prime[k], {k,1,Infinity} ]. C = limit[ a(n)/2^Prime[n], n->Infinity ] = 0.148809550788776224969568467866796531982224132808217067371770000563313912... Decimal expansion of Parity Prime Constant C is given in A122153[n]. Binary expansion of Primary Prime Constant C is given in A071986[n] = Mod[Pi[n], 2].
FORMULA
a(n) = Numerator[ Sum[ (-1)^(k+1) * 1/2^Prime[k], {k,1,n} ] ].
MATHEMATICA
Table[Numerator[Sum[(-1)^(k+1)*1/2^Prime[k], {k, 1, n}]], {n, 1, 30}]
CROSSREFS
KEYWORD
frac,nonn
AUTHOR
Alexander Adamchuk, Aug 22 2006
STATUS
approved