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 A212213 #22 Sep 06 2023 23:18:52
%S A212213 0,0,0,0,1,0,0,0,0,0,0,1,0,1,0,1,1,1,1,1,1,1,2,1,2,1,2,1,0,1,1,1,1,1,
%T A212213 1,0,0,1,1,2,1,2,1,1,0,0,0,0,1,1,1,1,0,0,0,0,1,0,1,1,2,1,1,0,1,0,1,1,
%U A212213 1,1,1,2,2,1,1,1,1,1,1,2,1,2,1,2,2,2,1,2,1,2,1,0,1,1,1,1,1,1,1,1,1,1,1,1,0
%N A212213 Array read by antidiagonals: pi(n) + pi(k) - pi(n+k), where pi() = A000720.
%C A212213 It is conjectured that pi(x) + pi(y) >= pi(x+y) for 1 < y <= x.
%D A212213 D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, Section VII.5, p. 235.
%H A212213 G. C. Greubel, <a href="/A212213/b212213.txt">Table of n, a(n) for the first 100 rows, flattened</a>
%H A212213 P. Erdős and J. L. Selfridge, <a href="http://www.renyi.hu/~p_erdos/1971-03.pdf">Complete prime subsets of consecutive integers</a>. Proceedings of the Manitoba Conference on Numerical Mathematics (Univ. Manitoba, Winnipeg, Man., 1971), pp. 1-14. Dept. Comput. Sci., Univ. Manitoba, Winnipeg, Man., 1971.
%e A212213 Array begins:
%e A212213 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, ...
%e A212213 0, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, ...
%e A212213 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, ...
%e A212213 0, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, ...
%e A212213 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, ...
%e A212213 1, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, ...
%e A212213 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, ...
%e A212213 ...
%t A212213 t[n_, k_] := PrimePi[n] + PrimePi[k] - PrimePi[n + k]; Table[t[n - k + 2, k], {n, 0, 15}, {k, 2, n}] // Flatten (* _Jean-François Alcover_, Dec 31 2012 *)
%Y A212213 Cf. A000720, A047885, A047886, A060208, A212210-A212213.
%K A212213 nonn,tabl,nice
%O A212213 2,23
%A A212213 _N. J. A. Sloane_, May 04 2012