

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
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OFFSET

0,2


COMMENTS

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


LINKS

Table of n, a(n) for n=0..24.


FORMULA

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


CROSSREFS

Cf. A006880.
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).
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.
Sequence in context: A086581 A059027 A025198 * A037247 A126221 A107086
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)


STATUS

approved



