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%I #14 Oct 28 2021 12:59:31
%S 1,3,19,146,1129,9142,77025,664277,5837665,52064915,469864125,
%T 4281198201,39319600765,363545360347,3380562309312,31590949437540,
%U 296487794277035,2793170342851930,26402713858800478,250324979315879678,2379753569255122805,22678735843184786383
%N Number of primes less than 10^n with initial digit 2.
%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)=3 because there are 3 primes up to 10^2 whose initial digit is 2 (namely 2, 23 and 29).
%t f[n_] := f[n] = PrimePi[3*10^n] - PrimePi[2*10^n] + f[n - 1]; f[0] = 1; Table[ f[n], {n, 0, 13}]
%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(21)-a(22) added by _David Baugh_, Mar 21 2015
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