OFFSET
1,1
COMMENTS
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
EXAMPLE
The semiprime 187=11*17 is in the sequence, because the average (11+17)/2=14 = 2*7 is semiprime.
The semiprime 267=3*89 is in the sequence because the average (3+89)/2=46=2*23 is semiprime.
MATHEMATICA
semiPrimeQ[n_] := Total[FactorInteger[n]][[2]] == 2; Reap[Do[{p, e} = Transpose[FactorInteger[n]]; If[Total[e] == 2 && semiPrimeQ[Total[p]/2], Sow[n]], {n, 1000}]][[2, 1]]
PROG
(PARI)sopf(n)= { local(f, s=0); f=factor(n); for(i=1, matsize(f)[1], s+=f[i, 1]); return(s) }
averg(n)={local(s); s=sopf(n)/omega(n); return(s)}
{ for (n=4, 10^3, m=averg(n); if(bigomega(n)==2, if(m==floor(m)&&bigomega(m)==2, print1(n, ", ")))) }
// Antonio Roldán, Oct 15 2012
(PARI) list(lim)=my(v=List()); forprime(p=3, lim\3, forprime(q=3, min(p-2, lim\p), if(bigomega((p+q)/2)==2, listput(v, p*q)))); Set(v) \\ Charles R Greathouse IV, Oct 16 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Antonio Roldán, Mar 09 2011
STATUS
approved