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 A257791 #14 Nov 05 2015 14:32:26
%S A257791 4,8,12,16,24,20,32,48,40,28,64,96,80,56,36,128,192,160,112,72,44,256,
%T A257791 384,320,224,144,88,52,512,768,640,448,288,176,104,60,1024,1536,1280,
%U A257791 896,576,352,208,120,68,2048,3072,2560,1792,1152,704,416,240,136,76
%N A257791 Rectangular array A read by upward antidiagonals in which the entry in row n and column k is defined by A(n,k) = 2^(n+1)*(2*k - 1), n,k >= 1.
%C A257791 Lemma: The sequence is a permutation of A008586\{0} = {4*m : m = 1,2,...}.
%C A257791 Proof: Write A(n,k)/4 = A054582(n-1,k-1). The sequence A054582 is known to be a permutation of the natural numbers, and the result follows. QED
%F A257791 A(n,n) = 4*A014480(n-1).
%e A257791 Array A begins:
%e A257791 . 4 12 20 28 36 44 52 60 68 76
%e A257791 . 8 24 40 56 72 88 104 120 136 152
%e A257791 . 16 48 80 112 144 176 208 240 272 304
%e A257791 . 32 96 160 224 288 352 416 480 544 608
%e A257791 . 64 192 320 448 576 704 832 960 1088 1216
%e A257791 . 128 384 640 896 1152 1408 1664 1920 2176 2432
%e A257791 . 256 768 1280 1792 2304 2816 3328 3840 4352 4864
%e A257791 . 512 1536 2560 3584 4608 5632 6656 7680 8704 9728
%e A257791 . 1024 3072 5120 7168 9216 11264 13312 15360 17408 19456
%e A257791 . 2048 6144 10240 14336 18432 22528 26624 30720 34816 38912
%t A257791 (* Array: *)
%t A257791 A257791[n_, k_] := 2^(n + 1)*(2*k - 1); Grid[Table[A257791[n, k], {n, 10}, {k, 10}]]
%t A257791 (* Array antidiagonals flattened: *)
%t A257791 Flatten[Table[2^(n - k + 2)*(2*k - 1), {n, 10}, {k, n}]]
%Y A257791 Cf. A000079 (powers of 2), A005408 (odd numbers), A008586 (multiples of 4), A014480, A054582.
%Y A257791 Cf. A257499.
%K A257791 nonn,tabl
%O A257791 1,1
%A A257791 _L. Edson Jeffery_, May 08 2015