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A221205 a(n) is the nearest integer to sqrt(pi(10^n)) (see A006880). 2
0, 2, 5, 13, 35, 98, 280, 815, 2400, 7131, 21332, 64172, 193928, 588273, 1790235, 5463018, 16710426, 51220671, 157289397, 483795067, 1490241458, 4596440959, 14193917243, 43878472986, 135777758736, 420530985064, 1303551591182, 4043817556078, 12553456467283 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Nearest integer to sqrt(pi(10^n)) where pi(10^n) is the number of primes < 10^n (A006880).

LINKS

Table of n, a(n) for n=0..28.

FORMULA

a(n) = round(sqrt(A006880(n))).

MATHEMATICA

Array[Round@ Sqrt@ PrimePi[10^#] &, 17, 0] (* Michael De Vlieger, Mar 19 2021 *)

PROG

(PARI) a(n) = round(sqrt(primepi(10^n))); \\ Michel Marcus, Mar 19 2021

CROSSREFS

Cf. A006880.

Sequence in context: A086581 A059027 A025198 * A037247 A308273 A126221

Adjacent sequences:  A221202 A221203 A221204 * A221206 A221207 A221208

KEYWORD

nonn,more

AUTHOR

Vladimir Pletser, Jan 04 2013

EXTENSIONS

a(21) to a(24) added by Vladimir Pletser, Feb 27 2013 (recovered by Georg Fischer, Jan 20 2019)

a(25)-a(28), obtained using A006880, added by Eduard Roure Perdices, Apr 16 2021

STATUS

approved

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Last modified October 21 08:06 EDT 2021. Contains 348150 sequences. (Running on oeis4.)