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 A338020 #26 Jan 31 2023 04:27:09
%S A338020 3,9,16,22,28,35,40,48,53,60,66,72,78,85,91,98,103,110,117,122,129,
%T A338020 135,141,148,154,160,167,173,179,185,192,197,205,210,217,223,229,236,
%U A338020 242,248,255,260,267,274,279,286,292,299,304,311,318,323,330,336,343,349,355,361,367
%N A338020 a(n) is the number of circles of positive integer area with radii less than n and greater than n - 1.
%C A338020 Conjecture: k >= 2, each triple Tr(k) = {a(k), a(k+1), a(k+2)} gives the sides of an integer-sided triangle, and {(a(k+2) - a(k)), (a(k+2) - a(k+1)), (a(k+1) - a(k))} is a degenerate integer-sided triangle.
%F A338020 a(n) = #{floor(sqrt(k/Pi)) < n: n > 0, k > 0}.
%F A338020 a(n) = A066643(n)-A066643(n-1). - _R. J. Mathar_, Jan 25 2023
%o A338020 (PARI) ap(n) = {my(x = 0, y = 1, ia = 1); while(y, if(n > sqrt(ia / Pi), x++; ia++, y = 0)); return(x)}
%o A338020 a(n) = {my(x = 0, y = 1, ia = 1); while(y, if(n > sqrt(ia / Pi), x++; ia++, y = 0)); return(x - ap(n-1))}
%o A338020 for(i = 1, 70, print1(a(i), ", "))
%Y A338020 Cf. A066643 (partial sums).
%K A338020 nonn
%O A338020 1,1
%A A338020 _Torlach Rush_, Oct 06 2020