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A279952 Number of primes with prime subscripts dividing n. 1
0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 2, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 2, 1, 0, 2, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 2, 0, 0, 1, 0, 1, 2, 0, 0, 1, 2, 0, 1, 0, 1, 2, 0, 1, 1, 0, 1, 2, 1, 1, 1, 1, 0, 1, 0, 0, 2, 0, 1, 1, 0, 1, 1, 1, 1, 1, 2, 0, 1, 1, 0, 2, 0, 0, 2, 0, 1, 1, 0, 0, 2, 1, 0, 2, 0, 0, 2, 0, 0, 1, 1, 2, 1, 0, 0, 1, 1, 0, 1, 1, 1, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,15

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

FORMULA

G.f.: Sum_{k>=1} x^prime(prime(k))/(1 - x^prime(prime(k))).

EXAMPLE

a(15) = 2 because 15 has 4 divisors {1,3,5,15} among which 2 divisors {3,5} are primes with prime subscripts.

MATHEMATICA

Rest[nmax = 120; CoefficientList[Series[Sum[x^Prime[Prime[k]]/(1 - x^Prime[Prime[k]]), {k, 1, nmax}], {x, 0, nmax}], x]]

PROG

(PARI) x='x+O('x^120); concat([0, 0], Vec(sum(k=1, 120, x^prime(prime(k))/(1 - x^prime(prime(k)))))) \\ Indranil Ghosh, May 23 2017

CROSSREFS

Cf. A001221, A006450.

Sequence in context: A164067 A305490 A113706 * A054845 A317991 A236853

Adjacent sequences:  A279949 A279950 A279951 * A279953 A279954 A279955

KEYWORD

nonn,easy

AUTHOR

Ilya Gutkovskiy, Dec 23 2016

STATUS

approved

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Last modified July 23 22:49 EDT 2019. Contains 325278 sequences. (Running on oeis4.)