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 A078435 #11 Oct 21 2024 04:56:31
%S A078435 1,2,5,10,16,25,34,46,59,75,91,110,130,152,177,202,228,258,289,322,
%T A078435 356,392,430,471,511,554,600,647,695,746,799,852,908,965,1025,1086,
%U A078435 1150,1216,1281,1349,1418,1490,1566,1641,1719,1797,1880,1962,2044,2133,2223
%N A078435 Number of composites <= n^2.
%F A078435 a(n) = n^2 - A038107(n). - _R. J. Mathar_, Jun 22 2009
%e A078435 a(3)=5 because the only composites <= 9 are 1, 4, 6, 8 and 9.
%p A078435 NumComposites := proc(N::posint) local count, i:count := 0:for i from 1 to N do if not isprime(i) then count := count + 1 fi:od: count;end:seq(NumComposites(k^2), k=1..51); # _Zerinvary Lajos_, May 26 2008
%p A078435 A038107 := proc(n) numtheory[pi]( n^2) ; end: A078435 := proc(n) n^2-A038107(n) ; end: seq(A078435(n),n=1..100) ; # _R. J. Mathar_, Jun 22 2009
%t A078435 a[n_] := n^2 - PrimePi[n^2];
%t A078435 Table[a[n], {n, 1, 100}] (* _Jean-François Alcover_, Oct 20 2024, after _R. J. Mathar_ *)
%K A078435 nonn
%O A078435 1,2
%A A078435 John E. Lenz (jel5010(AT)yahoo.com), Dec 30 2002