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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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.

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 A253654

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

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Last modified February 23 13:37 EST 2020. Contains 332159 sequences. (Running on oeis4.)