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 A257251 #23 Mar 08 2016 07:19:53
%S A257251 2,2,6,2,6,20,2,6,10,42,2,6,20,28,110,2,6,10,14,22,156,2,6,20,28,44,
%T A257251 52,272,2,6,10,14,22,26,34,342,2,6,20,28,44,52,68,76,506,2,6,10,42,66,
%U A257251 78,102,114,138,812,2,6,20,14,22,26,34,38,46,58,930,2,6,10,42,66,78,102,114,138,174,186,1332
%N A257251 Square array A(row,col) = A083221(row,col+1) - A083221(row,col): the first differences of each row of array constructed from the sieve of Eratosthenes.
%C A257251 The array is read by downwards antidiagonals as A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), ...
%H A257251 Antti Karttunen, <a href="/A257251/b257251.txt">Table of n, a(n) for n = 1..3321; the first 81 antidiagonals of the array</a>
%H A257251 <a href="/index/Si#sieve">Index entries for sequences generated by sieves</a>
%F A257251 A(row,col) = A083221(row,col+1) - A083221(row,col).
%F A257251 A(row,col) = 2*A257253(row,col).
%e A257251 The top left corner of the array:
%e A257251 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
%e A257251 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6
%e A257251 20, 10, 20, 10, 20, 10, 20, 10, 20, 10, 20, 10, 20, 10, 20
%e A257251 42, 28, 14, 28, 14, 28, 42, 14, 42, 28, 14, 28, 14, 28, 42
%e A257251 110, 22, 44, 22, 44, 66, 22, 66, 44, 22, 44, 66, 66, 22, 66
%e A257251 156, 52, 26, 52, 78, 26, 78, 52, 26, 52, 78, 78, 26, 78, 52
%e A257251 272, 34, 68, 102, 34, 102, 68, 34, 68, 102, 102, 34, 102, 68, 34
%e A257251 342, 76, 114, 38, 114, 76, 38, 76, 114, 114, 38, 114, 76, 38, 114
%e A257251 506, 138, 46, 138, 92, 46, 92, 138, 138, 46, 138, 92, 46, 138, 92
%e A257251 812, 58, 174, 116, 58, 116, 174, 174, 58, 174, 116, 58, 174, 116, 174
%e A257251 930, 186, 124, 62, 124, 186, 186, 62, 186, 124, 62, 186, 124, 186, 248
%e A257251 1332, 148, 74, 148, 222, 222, 74, 222, 148, 74, 222, 148, 222, 296, 148
%e A257251 1640, 82, 164, 246, 246, 82, 246, 164, 82, 246, 164, 246, 328, 164, 82
%e A257251 1806, 172, 258, 258, 86, 258, 172, 86, 258, 172, 258, 344, 172, 86, 172
%e A257251 2162, 282, 282, 94, 282, 188, 94, 282, 188, 282, 376, 188, 94, 188, 94
%e A257251 2756, 318, 106, 318, 212, 106, 318, 212, 318, 424, 212, 106, 212, 106, 212
%e A257251 ...
%t A257251 lim = 13; Clear[row]; row[n_] := row[n] = Take[Prime[n]*Select[Range[lim^2], GCD[#*Prime[n], Product[Prime[i], {i, n-1}]] == 1&], lim] // Differences;
%t A257251 A[n_, k_] := row[n][[k]]; Table[A[n-k+1, k], {n, 1, lim-1}, {k, n, 1, -1}] // Flatten (* _Jean-François Alcover_, Mar 08 2016, after _Michael De Vlieger_ in A083221 *)
%o A257251 (Scheme)
%o A257251 (define (A257251 n) (A257251bi (A002260 n) (A004736 n)))
%o A257251 (define (A257251bi row col) (- (A083221bi row (+ 1 col)) (A083221bi row col))) ;; Code for A083221bi given in A083221.
%Y A257251 Transpose: A257252.
%Y A257251 Column 1: A036689.
%Y A257251 Row 4: 7 * A145011.
%Y A257251 Cf. A083221, A257253 (same array but with terms divided by 2).
%Y A257251 Cf. arrays A257255 and A257257, also A257513.
%K A257251 nonn,tabl,look
%O A257251 1,1
%A A257251 _Antti Karttunen_, Apr 19 2015