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 A289869 #18 Mar 07 2025 16:13:28 %S A289869 0,2,1,6,3,3,8,7,5,4,18,9,9,6,9,20,19,11,10,11,10,24,21,21,12,15,12, %T A289869 12,26,25,23,22,17,16,14,13,54,27,27,24,27,18,18,15,27,56,55,29,28,29, %U A289869 28,20,19,29,28,60,57,57,30,33,30,30,21,33,30,30,62,61,59 %N A289869 Square array T(n,k) (n>=0, k>=0) read by antidiagonals downwards: T(n,k) = A005836(n) + 2*A005836(k). %C A289869 If n and k have no common one bit in base 2 representation (n AND k = 0), then n = A289813(T(n,k)) and k = A289814(T(n,k)). %C A289869 This sequence, when restricted to the pairs of numbers without common bits in base 2 representation, is the inverse of the function n -> (A289813(n), A289814(n)). %H A289869 Rémy Sigrist, <a href="/A289869/b289869.txt">First 100 antidiagonals of array, flattened</a> %e A289869 The table begins: %e A289869 x\y: 0 1 2 3 4 5 6 7 8 9 ... %e A289869 0: 0 2 6 8 18 20 24 26 54 56 ... %e A289869 1: 1 3 7 9 19 21 25 27 55 57 ... %e A289869 2: 3 5 9 11 21 23 27 29 57 59 ... %e A289869 3: 4 6 10 12 22 24 28 30 58 60 ... %e A289869 4: 9 11 15 17 27 29 33 35 63 65 ... %e A289869 5: 10 12 16 18 28 30 34 36 64 66 ... %e A289869 6: 12 14 18 20 30 32 36 38 66 68 ... %e A289869 7: 13 15 19 21 31 33 37 39 67 69 ... %e A289869 8: 27 29 33 35 45 47 51 53 81 83 ... %e A289869 9: 28 30 34 36 46 48 52 54 82 84 ... %e A289869 ... %o A289869 (PARI) T(n,k) = fromdigits(binary(n),3) + 2*fromdigits(binary(k),3) %o A289869 (Python) %o A289869 def T(n, k): return int(bin(n)[2:], 3) + 2*int(bin(k)[2:], 3) %o A289869 for n in range(11): print([T(k, n - k) for k in range(n + 1)]) # _Indranil Ghosh_, Aug 03 2017 %Y A289869 Cf. A005836, A289813, A289814. %K A289869 nonn,tabl,base %O A289869 1,2 %A A289869 _Rémy Sigrist_, Jul 14 2017