This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A221205 #37 Jul 31 2022 14:07:26 %S A221205 0,2,5,13,35,98,280,815,2400,7131,21332,64172,193928,588273,1790235, %T A221205 5463018,16710426,51220671,157289397,483795067,1490241458,4596440959, %U A221205 14193917243,43878472986,135777758736,420530985064,1303551591182,4043817556078,12553456467283,38996129419652 %N A221205 a(n) is the nearest integer to sqrt(pi(10^n)) (see A006880). %C A221205 Nearest integer to sqrt(pi(10^n)) where pi(10^n) is the number of primes < 10^n (A006880). %F A221205 a(n) = round(sqrt(A006880(n))). %t A221205 Array[Round@ Sqrt@ PrimePi[10^#] &, 17, 0] (* _Michael De Vlieger_, Mar 19 2021 *) %o A221205 (PARI) a(n) = round(sqrt(primepi(10^n))); \\ _Michel Marcus_, Mar 19 2021 %o A221205 (Python) %o A221205 from math import isqrt %o A221205 from sympy import primepi %o A221205 def A221205(n): return (m:=isqrt(k:=int(primepi(10**n))))+int(k-m*(m+1)>=1) # _Chai Wah Wu_, Jul 31 2022 %Y A221205 Cf. A006880. %K A221205 nonn %O A221205 0,2 %A A221205 _Vladimir Pletser_, Jan 04 2013 %E A221205 a(21) to a(24) added by _Vladimir Pletser_, Feb 27 2013 (recovered by _Georg Fischer_, Jan 20 2019) %E A221205 a(25)-a(28), obtained using A006880, added by _Eduard Roure Perdices_, Apr 16 2021 %E A221205 a(29), obtained using A006880, added by _Chai Wah Wu_, Jul 31 2022