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 A120319 RF(3): refactorable numbers with smallest prime factor 3. 0

%I

%S 9,225,441,1089,1521,2025,2601,3249,4761,5625,6561,7569,8649,12321,

%T 15129,16641,19881,25281,31329,33489,35721,40401,45369,47961,50625,

%U 56169,62001,71289,84681,91809,95481,99225,103041,106929,114921,145161

%N RF(3): refactorable numbers with smallest prime factor 3.

%C See A033950 for references. For any prime p, p^(p-1) is the smallest element of RF(p), the refactorable numbers whose smallest prime factor is p. Thus 3^(3-1)=9 is the first element. Other elements would also be 3^2*17^2 or 3^16*17^2.

%F a(n) = odd square, 3 is the smallest prime factor and refactorable.

%p with(numtheory); RF3:=[]: p:=3: for w to 1 do for j from 1 to 12^3 do k:=2*j+1; if k mod p = 0 then n:=k^2; t:=tau(n); if (n mod t = 0) then RF3:=[op(RF3),n]; print(ifactor(n)); fi fi; od od;

%Y Cf. A033950, A036896, A036897.

%K nonn

%O 1,1

%A _Walter Kehowski_, Jun 20 2006

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Last modified October 23 23:51 EDT 2019. Contains 328379 sequences. (Running on oeis4.)