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 A227798 #18 Mar 01 2018 02:32:00 %S A227798 499999999,166666666,66666666,38095237,20779220,15984016,11282834, %T A227798 9501331,7435826,5640969,5095068,4131143,3627360,3374293,3015292, %U A227798 2616982,2306411,2192860,1963654,1825278,1750219,1595163,1499127,1381337,1253379,1191536 %N A227798 Number of composites removed in each step of the Sieve of Eratosthenes for 10^9. %C A227798 a(n) = the number of composites <= 10^9 for which the n-th prime is the least prime factor. %C A227798 pi(sqrt(10^9)) = the number of terms of this sequence. %C A227798 The sum of a(n) for n = 1..3401 = A000720(10^9) + A065855(10^9). %H A227798 Eric F. O'Brien, <a href="/A227798/b227798.txt">Table of n, a(n) for n = 1..3401</a> %e A227798 a(1) = 10^9 \ 2 - 1. %e A227798 a(2) = 10^9 \ 3 - 10^9 \ (2*3) - 1 %e A227798 a(3) = 10^9 \ 5 - 10^9 \ (2*5) - 10^9 \ (3*5) + 10^9 \ (2*3*5) - 1 %e A227798 a(4) = 10^9 \ 7 - 10^9 \ (2*7) - 10^9 \ (3*7) - 10^9 \ (5*7) + 10^9 \ (2*3*7) + 10^9 \ (2*5*7) + 10^9 \ (3*5*7) - 10^9 \ (2*3*5*7) - 1. %Y A227798 Cf. A133228, A145538-A145540, A227155, A227797, A227799, A145532-A145537. %K A227798 nonn,fini,full %O A227798 1,1 %A A227798 _Eric F. O'Brien_, Jul 31 2013