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A120319 RF(3): refactorable numbers with smallest prime factor 3. 0
9, 225, 441, 1089, 1521, 2025, 2601, 3249, 4761, 5625, 6561, 7569, 8649, 12321, 15129, 16641, 19881, 25281, 31329, 33489, 35721, 40401, 45369, 47961, 50625, 56169, 62001, 71289, 84681, 91809, 95481, 99225, 103041, 106929, 114921, 145161 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..36.

FORMULA

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

MAPLE

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;

CROSSREFS

Cf. A033950, A036896, A036897.

Sequence in context: A033632 A110260 A036896 * A057530 A014736 A017558

Adjacent sequences:  A120316 A120317 A120318 * A120320 A120321 A120322

KEYWORD

nonn

AUTHOR

Walter Kehowski, Jun 20 2006

STATUS

approved

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Last modified September 20 08:13 EDT 2019. Contains 327214 sequences. (Running on oeis4.)