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A343732
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Numbers k at which tau(k^k) is a prime power, where tau is the number-of-divisors function A000005.
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1
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2, 3, 4, 6, 7, 8, 9, 10, 15, 22, 26, 30, 31, 36, 42, 46, 58, 66, 70, 78, 82, 102, 106, 121, 127, 130, 138, 166, 178, 190, 210, 222, 226, 238, 255, 262, 282, 310, 330, 346, 358, 366, 382, 418, 430, 438, 441, 442, 462, 466, 478, 498, 502, 511, 546, 562, 570, 586
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OFFSET
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1,1
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LINKS
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EXAMPLE
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9^9 = (3^2)^9 = 3^18 has 19 = 19^1 divisors, so 9 is a term.
10^10 = 2^10 * 5^10 has 121 = 11^2 divisors, so 10 is a term.
11^11 has 12 = 2^2 * 3^1 divisors, so 11 is not a term.
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MATHEMATICA
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a={}; For[k=1, k<600, k++, If[PrimePowerQ[DivisorSigma[0, k^k]], AppendTo[a, k]]]; a (* Stefano Spezia, Jun 02 2021 *)
Select[Range[600], PrimePowerQ[DivisorSigma[0, #^#]]&] (* Harvey P. Dale, Oct 29 2022 *)
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PROG
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(PARI) isok(k) = isprimepower(numdiv(k^k)); \\ Michel Marcus, Jun 02 2021
(Python)
from functools import reduce
from operator import mul
from sympy import factorint
A343732_list = [n for n in range(2, 10**3) if len(factorint(reduce(mul, (n*d+1 for d in factorint(n).values())))) == 1] # Chai Wah Wu, Jun 03 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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