OFFSET
1,1
COMMENTS
Subsequence of A225228. - Reinhard Zumkeller, May 03 2013
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
Will Nicholes, List of prime signatures, 2010.
FORMULA
A050326(a(n)) = 5. - Reinhard Zumkeller, May 03 2013
Sum_{n>=1} 1/a(n) = P(2)^2*P(3)/2 - P(3)*P(4)/2 - P(2)*P(5) + P(7) = 0.0032578591481263202818..., where P is the prime zeta function. - Amiram Eldar, Mar 07 2024
MATHEMATICA
f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 2, 3}; Select[Range[10^5], f]
f[n_]:={Times@@(n^{2, 2, 3}), Times@@(n^{2, 3, 2}), Times@@(n^{3, 2, 2})}; Module[ {nn=20}, Select[Flatten[f/@Subsets[Prime[Range[nn]], {3}]], #<= 72*Prime[ nn]^2&]]//Union (* Harvey P. Dale, Jul 05 2019 *)
PROG
(PARI) list(lim)=my(v=List(), t1, t2); forprime(p=2, (lim\36)^(1/3), t1=p^3; forprime(q=2, sqrt(lim\t1), if(p==q, next); t2=t1*q^2; forprime(r=q+1, sqrt(lim\t2), if(p==r, next); listput(v, t2*r^2)))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 24 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jul 24 2010
STATUS
approved