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A221205
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a(n) is the nearest integer to sqrt(pi(10^n)) (see A006880).
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3
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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, 38996129419652
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OFFSET
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0,2
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COMMENTS
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Nearest integer to sqrt(pi(10^n)) where pi(10^n) is the number of primes < 10^n (A006880).
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LINKS
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FORMULA
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MATHEMATICA
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PROG
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(PARI) a(n) = round(sqrt(primepi(10^n))); \\ Michel Marcus, Mar 19 2021
(Python)
from math import isqrt
from sympy import primepi
def A221205(n): return (m:=isqrt(k:=int(primepi(10**n))))+int(k-m*(m+1)>=1) # Chai Wah Wu, Jul 31 2022
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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