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).

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, 21, 19, 128, 96, 72, 54, 40, 30, 22, 23, 256, 192, 144, 108, 80, 56, 42, 26, 25, 512, 384, 288, 216, 160, 81, 60, 44, 33, 29, 1024, 768, 576, 432, 320, 162, 112, 84, 45, 34, 31

Offset: 1

Author

Robert G. Wilson v, Dec 19 2009

Keywords

• nonn
• tabl

Examples

			The array starts in row n=0 as:
1, 5, 7, 11, 13, 17, 19, 23, 25, 29: not divisible by 2 or 3
2, 3, 10, 14, 15, 21, 22, 26, 33, 34: divisible by 2^i*3^(1-i), i<=1
4, 6, 9, 20, 28, 30, 42, 44, 45, 52: divisible by 2^i*3^(2-i), i<=2
8, 12, 18, 27, 40, 56, 60, 84, 88, 90: divisible by 2^i*3^(3-i): i<=3
16, 24, 36, 54, 80, 81, 112, 120, 168, 176
32, 48, 72, 108, 160, 162, 224, 240, 243, 336
64, 96, 144, 216, 320, 324, 448, 480, 486, 672
		

Crossrefs

Cf. A169611, A171126, A171127.

Programs

Mathematica

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