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 A289053 #21 Jun 26 2017 08:01:00
%S A289053 1,3,2,9,6,4,17,13,7,5,40,26,19,11,8,56,48,31,23,15,10,90,75,61,39,28,
%T A289053 18,12,114,103,79,68,44,34,20,14,164,135,122,94,81,54,37,24,16,253,
%U A289053 199,172,152,118,101,65,49,30,21
%N A289053 Array T(i,k) read by antidiagonals: position of prime(i)*prime(k) in A001358.
%e A289053 Array begins:
%e A289053 1 2 4 5 8 10 12 14 16 21
%e A289053 3 6 7 11 15 18 20 24 30
%e A289053 9 13 19 23 28 34 37 49
%e A289053 17 26 31 39 44 54 65
%e A289053 40 48 61 68 81 101
%e A289053 56 75 79 94 118
%e A289053 90 103 122 152
%e A289053 114 135 172
%e A289053 164 199
%e A289053 253
%t A289053 With[{nn = 11}, Function[s, Table[Position[s, Prime[i] Prime[k]][[1, 1]], {i, nn}, {k, i, 1, -1}] // Flatten]@ Select[Range[Prime[nn]^2], PrimeOmega@ # == 2 &]] (* _Michael De Vlieger_, Jun 23 2017 *)
%Y A289053 Cf. A000040, A001358, A115392 (1st row), A128301 (1st column).
%K A289053 nonn,tabl
%O A289053 1,2
%A A289053 _Zak Seidov_, Jun 23 2017