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A133498 a(n) = floor(sqrt(pi(2^n))). 1
0, 1, 1, 2, 2, 3, 4, 5, 7, 9, 13, 17, 23, 32, 43, 59, 80, 110, 151, 208, 286, 394, 544, 751, 1038, 1436, 1989, 2757, 3825, 5309, 7375, 10251, 14257, 19839, 27621, 38473, 53613, 74742, 104241, 145436, 202985, 283401, 395804, 552957, 772733, 1080160, 1510297 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..86

FORMULA

a(n) = floor(sqrt(A007053(n))).

EXAMPLE

a(4)=2 because pi(2^4)=6 and the greatest integer less than or equal to sqrt(6) is 2.

MATHEMATICA

Table[ Floor[Sqrt[PrimePi[2^n]]], {n, 0, 25}] (* G. C. Greubel, Jan 13 2017 *)

PROG

(PARI) a(n) = sqrtint(primepi(2^n)); \\ Michel Marcus, Sep 05 2013

CROSSREFS

Cf. A000720, A007053.

Sequence in context: A032277 A205579 A089047 * A282949 A292200 A249576

Adjacent sequences:  A133495 A133496 A133497 * A133499 A133500 A133501

KEYWORD

nonn

AUTHOR

Andrew V. Sutherland, Dec 01 2007

STATUS

approved

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Last modified June 24 01:22 EDT 2018. Contains 311819 sequences. (Running on oeis4.)