A087053 Numbers of the form pq + qr + rp where p, q and r are distinct primes, with multiplicity.

31, 41, 61, 59, 71, 91, 71, 87, 101, 101, 121, 113, 103, 129, 151, 131, 161, 143, 119, 191, 171, 131, 167, 211, 151, 221, 185, 151, 241, 167, 191, 213, 227, 271, 221, 199, 301, 191, 311, 269, 243, 167, 211, 341, 275, 297, 269, 361, 215, 311, 293, 247, 371

Offset

1,1

Comments

Arithmetic derivative of numbers having exactly three primes that are distinct: a(n) = A003415(A007304(n)).

Links

Table of n, a(n) for n=1..53.

Prog

(PARI) is(n)=forprime(r=(sqrtint(3*n-3)+5)\3, (n-6)\5, forprime(q= sqrtint(r^2+n)-r+1, min((n-2*r)\(r+2), r-2), if((n-q*r)%(q+r)==0 && isprime((n-q*r)/(q+r)), return(1)))); 0 \\ Charles R Greathouse IV, Feb 26 2014
(PARI) list(n)=my(v=List()); forprime(r=5, (n-6)\5, forprime(q=3, min((n-2*r)\(r+2), r-2), my(S=q+r, P=q*r); forprime(p=2, min((n-P)\S, q-1), listput(v, p*S+P))));  Set(v) \\ Charles R Greathouse IV, Feb 26 2014

Crossrefs

Cf. A087054, A238397.

Sequence in context: A245650 A363187 A098711 * A159045 A099181 A040989

Adjacent sequences: A087050 A087051 A087052 * A087054 A087055 A087056

Keyword

nonn

Author

Reinhard Zumkeller, Aug 07 2003

Status

approved