A096916 Lesser prime factor of n-th product of two distinct primes.

2, 2, 2, 3, 3, 2, 2, 3, 2, 5, 2, 3, 2, 3, 5, 3, 2, 2, 5, 3, 2, 7, 2, 5, 2, 3, 7, 3, 2, 5, 2, 3, 5, 2, 7, 2, 3, 3, 7, 2, 3, 2, 11, 5, 2, 5, 2, 3, 7, 2, 3, 2, 3, 5, 11, 2, 3, 2, 7, 5, 2, 11, 3, 2, 5, 7, 2, 3, 13, 2, 5, 3, 13, 3, 11, 2, 7, 2, 5, 3, 2, 2, 7, 3, 5, 2, 13, 7, 2, 3, 5, 3, 2, 11, 3, 17, 2, 3

Offset: 1

Author

Reinhard Zumkeller, Jul 15 2004

Keywords

• nonn
• look

Comments

a(n)*A070647(n) = A006881(n); a(n) < A070647(n);

a(n) = A020639(A006881(n)).

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A084126, A195758.

Programs

Haskell

a096916 = a020639 . a006881 -- Reinhard Zumkeller, Sep 23 2011

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1,1};f1[n_]:=Min[First/@FactorInteger[n]];f2[n_]:=Max[First/@FactorInteger[n]];lst={};Do[If[f[n],AppendTo[lst,f1[n]]],{n,0,6!}];lst (* Vladimir Joseph Stephan Orlovsky, Apr 10 2010 *)

PARI

go(x)=my(v=List()); forprime(p=2, sqrtint(x\1), forprime(q=p+1, x\p, listput(v, [p*q,p]))); apply(v->v[2], vecsort(Vec(v),1)) \\ Charles R Greathouse IV, Sep 14 2015