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%I #11 Oct 28 2021 12:59:31
%S 0,2,18,135,1013,8458,72257,628206,5556434,49815418,451476802,
%T 4128049326,38024311091,352446754137,3284400373590,30749731897370,
%U 289066731934716,2727216210298152,25812680778645432,245015325044029789,2331718909954888809,22242097596092999144
%N Number of primes less than 10^n with initial digit 6.
%H Thomas R. Nicely, <a href="https://faculty.lynchburg.edu/~nicely/index.html">Some Results of Computational Research in Prime Numbers</a> [See local copy in A007053]
%H Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/primes.html">Tables of values of pi(x) and of pi2(x)</a>
%e a(2)=2 because there are 2 primes up to 10^2 whose initial digit is 2 (namely 61 and 67).
%t f[n_] := f[n] = PrimePi[7*10^n] - PrimePi[6*10^n] + f[n - 1]; f[0] = 0; Table[ f[n], {n, 0, 12}]
%Y Cf. A073509 to A073517, their sum is A006880.
%Y For primes with initial digit d (1 <= d <= 9) see A045707, A045708, A045709, A045710, A045711, A045712, A045713, A045714, A045715; A073517, A073516, A073515, A073514, A073513, A073512, A073511, A073510, A073509
%K base,hard,nonn
%O 1,2
%A _Shyam Sunder Gupta_, Aug 14 2002
%E Edited and extended by _Robert G. Wilson v_, Aug 29 2002
%E a(20)-a(22) added by _David Baugh_, Mar 22 2015
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