OFFSET
1,4
COMMENTS
Roughly analogous to Least Prime Factor A020639 but with semiprimes rather than primes.
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
FORMULA
EXAMPLE
a(24) = 4 because 24 is divisible by the semiprimes {4,6} of which 4 is the smallest.
MATHEMATICA
Table[If[PrimeQ[n] || n < 2, 0, f = FactorInteger[n]; If[f[[1, 2]] > 1, f[[1, 1]]^2, f[[1, 1]]*f[[2, 1]]]], {n, 100}] (* T. D. Noe, Mar 24 2012 *)
Flatten[Table[Select[Divisors[n], PrimeOmega[#]==2&, 1], {n, 80}]/.{}->{0}] (* Harvey P. Dale, Dec 07 2012 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Mar 23 2012
STATUS
approved