0,3

Or primepi(10^(n/4)).

Table of n, a(n) for n=0..39.

a(1) = 0 because 10^(1/4) = 1.77828... and there are no primes less than that.

a(2) = 2 because sqrt(10) = 3.16228... and there are 2 primes below that.

a(3) = 3 because 10^(3/4) = 5.62341... and there are 3 primes below that.

Table[PrimePi[10^(n/4)], {n, 0, 39}] (* Alonso del Arte, Jan 26 2013 *)

Cf. A006880, A018072.

Sequence in context: A196382 A120415 A023361 * A113435 A222022 A025048

Adjacent sequences: A210515 A210516 A210517 * A210519 A210520 A210521

nonn,hard

Vladimir Pletser, Jan 26 2013

approved