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%I #7 Jul 20 2019 11:13:06
%S 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,
%T 24,54,25,26,27,28,98,29,30,31,32,33,34,35,36,37,38,39,40,250,41,42,
%U 43,44,242,45,75,46,47,48,162,49,20,50,51,52,338,53,24,54,55
%N 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.
%C If n is a perfect power of a squarefree number then it contributes only one term.
%e 18 follows 12 as 12=2^2*3 and 18 = 3^2*2.
%t 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 *)
%K easy,nonn,tabf
%O 1,2
%A _Amarnath Murthy_, Aug 05 2005
%E More terms from _Amiram Eldar_, Jul 20 2019
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