A167184 Smallest prime power >= n that is not prime.
1, 4, 4, 4, 8, 8, 8, 8, 9, 16, 16, 16, 16, 16, 16, 16, 25, 25, 25, 25, 25, 25, 25, 25, 25, 27, 27, 32, 32, 32, 32, 32, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 81, 81, 81, 81, 81, 81, 81, 81
Offset: 1
Examples
For a(12), 12, 14, and 15 are not prime powers, and 13 is a prime power but it is prime. Since 16 = 2^4 is a prime power, a(12) = 16.
Links
- Robert Price, Table of n, a(n) for n = 1..2000
Crossrefs
Programs
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Mathematica
Module[{ppwrs=Join[{1},Sort[Flatten[Table[Prime[Range[5]]^p,{p,2,10}]]]]}, Flatten[ Table[Select[ppwrs,#>=n&,1],{n,90}]]] (* Harvey P. Dale, Oct 06 2014 *) -
PARI
isA025475(n) = (omega(n) == 1 & !isprime(n)) || (n == 1) A167184(n) = {local(m);m=n;while(!isA025475(m),m++);m}
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Python
from itertools import count from sympy import factorint def A167184(n): return next(filter(lambda m:len(f:=factorint(m))<=1 and max(f.values(),default=2)>1, count(n))) # Chai Wah Wu, Oct 25 2024
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