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A087053 Numbers of the form pq + qr + rp where p, q and r are distinct primes, with multiplicity. 5
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 (list; graph; refs; listen; history; text; internal format)
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: A087054 A245650 A098711 * A159045 A099181 A040989

Adjacent sequences:  A087050 A087051 A087052 * A087054 A087055 A087056

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Aug 07 2003

STATUS

approved

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Last modified September 29 05:48 EDT 2020. Contains 337425 sequences. (Running on oeis4.)