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A073505
Number of primes == 1 (mod 10) less than 10^n.
5
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
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}]
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