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A073511 Number of primes less than 10^n with initial digit 7. 23

%I

%S 1,4,18,125,1027,8435,71564,622882,5516130,49495432,448855139,

%T 4106164356,37838546363,350849788546,3270531245684,30628143485953,

%U 287992070079777,2717649138419586,25726964404879666,244242934202964444,2324722877951987037,22178433287546997612

%N Number of primes less than 10^n with initial digit 7.

%H Thomas R. Nicely, <a href="http://www.trnicely.net/index.html">Some Results of Computational Research in Prime Numbers</a>

%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)=4 because there are 4 primes up to 10^2 whose initial digit is 7 (namely 7, 71, 73 and 79).

%t f[n_] := f[n] = PrimePi[8*10^n] - PrimePi[7*10^n] + f[n - 1]; f[0] = 1; 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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Last modified February 18 02:57 EST 2020. Contains 332006 sequences. (Running on oeis4.)