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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. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified July 2 14:41 EDT 2020. Contains 335401 sequences. (Running on oeis4.)