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 A221205 a(n) is the nearest integer to sqrt(pi(10^n)) (see A006880). 2

%I

%S 0,2,5,13,35,98,280,815,2400,7131,21332,64172,193928,588273,1790235,

%T 5463018,16710426,51220671,157289397,483795067,1490241458,4596440959,

%U 14193917243,43878472986,135777758736

%N a(n) is the nearest integer to sqrt(pi(10^n)) (see A006880).

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

%C The series of terms 2, 5, 13, 35, 98 is found in many other sequences (see crossrefs) while the following terms have values close to those of most of these other sequences.

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

%Y Cf. A006880.

%Y The series of terms 2, 5, 13, 35, 98 are found in (for n = 1 to 5) A126221 and (for n = 3 to 7) in A037247 (with absolute values).

%Y The series of terms 2, 5, 13, 35 are found in (for n = 0 to 3) A007689, A000747; (for n = 1 to 4) A221214, A085810, A057960, A085281, A137674, A024576, A048781, A126221, A007075, A025198, A054657, A149853; (for n = 2 to 5) A005773, A000107, A086581, A160438, A059027, A089846, A091190, A097919, A022855, A148291, A148292, A148293, A148294, A148295, A151259; (for n = 3 to 6) A025242, A082582, A131868, A063028 and A107086 and A037247 (with absolute values); (for n = 37 to 40) A210877; (for n = 46 to 49) A209690; and (for n = 47 to 50) A210873.

%K nonn,more

%O 0,2

%A _Vladimir Pletser_, Jan 04 2013

%E a(21) to a(24) added by _Vladimir Pletser_, Feb 27 2013 (recovered by _Georg Fischer_, Jan 20 2019)

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Last modified May 23 07:08 EDT 2019. Contains 323508 sequences. (Running on oeis4.)