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The October issue of the Notices of the Amer. Math. Soc. has an article about the OEIS.

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A249058 a(n) = number of primes less than the square root of the (2^n)-th prime 2
0, 0, 1, 2, 4, 5, 7, 9, 12, 17, 24, 32, 45, 61, 82, 114, 154, 215, 293, 404, 557, 766, 1057, 1459, 2025, 2800, 3880, 5379, 7470, 10368, 14414, 20030, 27864, 38745, 53982, 75206, 104799, 146151, 203821, 284381, 396976, 554303, 774256, 1081749, 1511871, 2113506 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Jens Kruse Andersen, Table of n, a(n) for n = 0..56

FORMULA

a(n) = primepi(sqrt(A033844(n))). - Jens Kruse Andersen, Oct 20 2014

MATHEMATICA

PrimePi[Sqrt[Prime[2^n]]]

CROSSREFS

Cf. A033844. Related to analysis of A247665.

Sequence in context: A069355 A212661 A288511 * A105771 A193494 A161832

Adjacent sequences:  A249055 A249056 A249057 * A249059 A249060 A249061

KEYWORD

nonn

AUTHOR

Russ Cox, Oct 19 2014

EXTENSIONS

More terms from Jens Kruse Andersen, Oct 20 2014

STATUS

approved

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Last modified September 22 17:05 EDT 2018. Contains 315270 sequences. (Running on oeis4.)