A073513 -id:A073513 - cp's OEIS frontend

A073507 Number of primes == 7 (mod 10) less than 10^n.

1, 6, 46, 308, 2411, 19621, 166211, 1440495, 12712314, 113764039, 1029518337, 9401997000, 86516367790

Offset: 1

Shyam Sunder Gupta, Aug 14 2002

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.

			a(2)=6 because there are 6 primes == 7 (mod 10) less than 10^2. They are 7, 17, 37, 47, 67 and 97.

Cf. A006880, A087632, A073505, A073506, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.

c = 0; k = 7; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}]

A073505(n) + A073506(n) + a(n) + A073508(n) + 2 = A006880(n).

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

A073508 Number of primes == 9 (mod 10) less than 10^n.

Original entry on oeis.org

0, 5, 38, 303, 2390, 19593, 166032, 1440186, 12711333, 113761326, 1029509896, 9401974132, 86516371101

Offset: 1

Shyam Sunder Gupta, Aug 14 2002

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.

			a(2) = 5 because there are 5 primes == 9 (mod 10) less than 10^2. They are 19, 29, 59, 79 and 89.

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

Cf. A006880, A087633, A073505, A073506, A073507, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.

c = 0; k = 9; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}]

A073505(n) + A073506(n) + A073507(n) + a(n) + 2 = A006880(n).

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

cp's OEIS Frontend

A073507 Number of primes == 7 (mod 10) less than 10^n.

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