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A171837 Array g(n,k) read by antidiagonals: the k-th integer with prime factorization 2^i * 3^(n-i) * 5^e_5 *7^e_7 * (... higher primes).

%I A171837 #4 Dec 10 2016 16:42:51
%S A171837 1,2,5,4,3,7,8,6,10,11,16,12,9,14,13,32,24,18,20,15,17,64,48,36,27,28,
%T A171837 21,19,128,96,72,54,40,30,22,23,256,192,144,108,80,56,42,26,25,512,
%U A171837 384,288,216,160,81,60,44,33,29,1024,768,576,432,320,162,112,84,45,34,31
%N A171837 Array g(n,k) read by antidiagonals: the k-th integer with prime factorization 2^i * 3^(n-i) * 5^e_5 *7^e_7 * (... higher primes).
%e A171837 The array starts in row n=0 as:
%e A171837 1, 5, 7, 11, 13, 17, 19, 23, 25, 29: not divisible by 2 or 3
%e A171837 2, 3, 10, 14, 15, 21, 22, 26, 33, 34: divisible by 2^i*3^(1-i), i<=1
%e A171837 4, 6, 9, 20, 28, 30, 42, 44, 45, 52: divisible by 2^i*3^(2-i), i<=2
%e A171837 8, 12, 18, 27, 40, 56, 60, 84, 88, 90: divisible by 2^i*3^(3-i): i<=3
%e A171837 16, 24, 36, 54, 80, 81, 112, 120, 168, 176
%e A171837 32, 48, 72, 108, 160, 162, 224, 240, 243, 336
%e A171837 64, 96, 144, 216, 320, 324, 448, 480, 486, 672
%t A171837 f[n_] := Plus @@ Last /@ Select[FactorInteger@n, 1 < #[[1]] < 4 &]; g[n_, k_] := Select [Range@ 1100, f@# == n &][[k]]; Table[g[n - k, k], {n, 11}, {k, n}] // Flatten
%Y A171837 Cf. A169611, A171126, A171127.
%K A171837 nonn,tabl
%O A171837 1,2
%A A171837 _Robert G. Wilson v_, Dec 19 2009