A073505 Number of primes == 1 (mod 10) less than 10^n.

0, 5, 40, 306, 2387, 19617, 166104, 1440298, 12711386, 113761519, 1029517130, 9401960980, 86516370000

Offset

1,2

Comments

Also Pi(n,5,1)

This and the related sequences A073505-A073517 and A006880, A073548-A073565 are included because there is interest in the distribution of primes by their initial or final digits.

Links

Table of n, a(n) for n=1..13.

Eric Weisstein's World of Mathematics, Modular Prime Counting Function

Formula

a(n) + A073506(n) + A073507(n) + A073508(n) + 2 = A006880(n).

Example

a(2) = 5 because there are 5 primes == 1 (mod 10) less than 10^2. They are 11, 31, 41, 61 and 71.

Mathematica

c = 0; k = 1; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}]

Crossrefs

Cf. A006880, A087630, A073506, A073507, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.

Sequence in context: A125729 A144069 A280158 * A145841 A123943 A067412

Adjacent sequences: A073502 A073503 A073504 * A073506 A073507 A073508

Keyword

base,nonn,more

Author

Shyam Sunder Gupta, Aug 14 2002

Extensions

Edited by Robert G. Wilson v, Oct 03 2002

a(10) from Robert G. Wilson v, Dec 22 2003

a(11)-a(13) from Giovanni Resta, Aug 07 2018

Status

approved