OFFSET
1,1
COMMENTS
A subsequence of A169834. - M. F. Hasler, Oct 26 2014
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..10000
Wikipedia, Semiprime
FORMULA
a(n) = A039833(n) + 1. - Michel Marcus, Oct 25 2014
a(n) = 2 * A195685(n). - Torlach Rush, Jun 25 2021
EXAMPLE
33, 34 and 35 factor as 3*11, 2*17 and 5*7, respectively. No smaller such trio exists, so a(1)=34.
MATHEMATICA
lst={}; Do[z=n^3 + 3 n^2 + 2 n; If[PrimeOmega[z/n]==PrimeOmega[z/(n + 2)]==4 && PrimeNu[z]==6, AppendTo[lst, n + 1]], {n, 1, 6000, 2}]; lst (* Vincenzo Librandi, Jul 24 2015 *)
SequencePosition[Table[If[SquareFreeQ[n]&&PrimeOmega[n]==2, 1, 0], {n, 4500}], {1, 1, 1}][[All, 1]]+1 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 11 2018 *)
PROG
(PARI) sq(n)=bigomega(n)==2 && omega(n)==2;
for(n=3, 10^4, if(sq(n-1)&&sq(n)&&sq(n+1), print1(n, ", ")));
\\ Joerg Arndt, Oct 18 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
James G. Merickel, Oct 03 2014
STATUS
approved