This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A073507 #15 Aug 07 2018 11:20:54
%S A073507 1,6,46,308,2411,19621,166211,1440495,12712314,113764039,1029518337,
%T A073507 9401997000,86516367790
%N A073507 Number of primes == 7 (mod 10) less than 10^n.
%C A073507 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.
%F A073507 A073505(n) + A073506(n) + a(n) + A073508(n) + 2 = A006880(n).
%e A073507 a(2)=6 because there are 6 primes == 7 (mod 10) less than 10^2. They are 7, 17, 37, 47, 67 and 97.
%t A073507 c = 0; k = 7; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}]
%Y A073507 Cf. A006880, A087632, A073505, A073506, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.
%K A073507 base,nonn,more
%O A073507 1,2
%A A073507 _Shyam Sunder Gupta_, Aug 14 2002
%E A073507 Edited by _Robert G. Wilson v_, Oct 03 2002
%E A073507 a(10) from _Robert G. Wilson v_, Dec 22 2003
%E A073507 a(11)-a(13) from _Giovanni Resta_, Aug 07 2018