

A073507


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


4



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

1,2


COMMENTS

This and the related sequences A073505A073517 and A006880, A073548A073565 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.


FORMULA

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


EXAMPLE

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


MATHEMATICA

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


CROSSREFS

Cf. A006880, A087632, A073505, A073506, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.
Sequence in context: A103768 A325947 A240779 * A155598 A190005 A334609
Adjacent sequences: A073504 A073505 A073506 * A073508 A073509 A073510


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



