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 A377181 #6 Oct 19 2024 22:13:40
%S A377181 4,6,9,8,12,16,9,15,21,26,10,16,25,33,39,12,18,26,38,49,56,14,21,28,
%T A377181 39,55,69,78,15,24,33,42,56,77,94,106,16,25,36,49,60,78,105,125,141,
%U A377181 18,26,38,52,69,84,106,140,164,184,20,28,39,55,74,94,115,141,183,212,236
%N A377181 Rectangular array, by antidiagonals: (row 1) = r(1) = A002808 (composite numbers); (row n) = r(n) = A002808(r(n-1)) for n>=1.
%F A377181 A059981(n) = number of appearances of A002808(n).
%e A377181 corner:
%e A377181 4 6 8 9 10 12 14 15 16 18
%e A377181 9 12 15 16 18 21 24 25 26 28
%e A377181 16 21 25 26 28 33 36 38 39 42
%e A377181 26 33 38 39 42 49 52 55 56 60
%e A377181 39 49 55 56 60 69 74 77 78 84
%e A377181 56 69 77 78 84 94 100 105 106 115
%e A377181 78 94 105 106 115 125 133 140 141 152
%t A377181 c[n_] := c[n] = Select[Range[500], CompositeQ][[n]]
%t A377181 r[0] = Table[c[n], {n, 1, 10}]
%t A377181 r[n_] := r[n] = c[r[n - 1]]
%t A377181 Grid[Table[r[n], {n, 0, 6}]] (* array *)
%t A377181 p[n_, k_] := r[n][[k]];
%t A377181 Table[p[n - k + 1, k], {n, 0, 9}, {k, n + 1, 1, -1}] // Flatten (* sequence *)
%Y A377181 Cf. A002808 (row 1), A050545 (row 2), A280327 (row 3), A006508 (column 1), A022450 (column 2), A023451 (column 3), A059981, A236356, A280327 (principal diagonal), A377173, A114577 (dispersion of the composite numbers).
%K A377181 nonn,tabl
%O A377181 1,1
%A A377181 _Clark Kimberling_, Oct 19 2024