A111470 - OEIS

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

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OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..67.

EXAMPLE

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

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 *)

CROSSREFS

Sequence in context: A276393 A193457 A161950 * A227508 A246200 A262356

Adjacent sequences: A111467 A111468 A111469 * A111471 A111472 A111473

KEYWORD

easy,nonn,tabf

AUTHOR

Amarnath Murthy, Aug 05 2005

EXTENSIONS

More terms from Amiram Eldar, Jul 20 2019

STATUS

approved