A073506 - OEIS

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A073506

Number of primes == 3 (mod 10) less than 10^n.

1, 7, 42, 310, 2402, 19665, 166230, 1440474, 12712499, 113765625, 1029509448, 9401979904, 86516427946

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OFFSET

1,2

COMMENTS

Also Pi(n,5,3)

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

A073505(n) + a(n) + A073507(n) + A073508(n) + 2 = A006880(n).

EXAMPLE

a(2)=7 because there are 7 primes == 3 (mod 10) less than 10^2. They are 3, 13, 23, 43, 53, 73 and 83.

MATHEMATICA

c = 0; k = 3; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}]

CROSSREFS

Cf. A006880, A087631, A073505, A073507, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.

Sequence in context: A366222 A332082 A271427 * A025593 A218124 A048862

Adjacent sequences: A073503 A073504 A073505 * A073507 A073508 A073509

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