A111470 Irregular table read by rows: the n-th row gives all the numbers with the prime signature of n using only prime divisors of n.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 18, 13, 14, 15, 16, 17, 18, 12, 19, 20, 50, 21, 22, 23, 24, 54, 25, 26, 27, 28, 98, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 250, 41, 42, 43, 44, 242, 45, 75, 46, 47, 48, 162, 49, 20, 50, 51, 52, 338, 53, 24, 54, 55

Offset: 1

Author

Amarnath Murthy, Aug 05 2005

Keywords

• easy
• nonn
• tabf

Comments

If n is a perfect power of a squarefree number then it contributes only one term.

Examples

			18 follows 12 as 12=2^2*3 and 18 = 3^2*2.
		

Programs

Mathematica

a[n_] := Module[{f = FactorInteger[n]}, p = f[[;; , 1]]; e = f[[;; , 2]]; Times @@ Power[p, #] & /@ Permutations[e]]; s = {}; Do[s = Join[s, a[n]], {n, 1, 55}]; s (* Amiram Eldar, Jul 20 2019 *)

Extensions

More terms from Amiram Eldar, Jul 20 2019