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A179690 Numbers of the form p^2*q^2*r*s where p, q, r, and s are distinct primes. 7
1260, 1980, 2100, 2340, 2772, 2940, 3060, 3150, 3276, 3300, 3420, 3900, 4140, 4284, 4410, 4788, 4950, 5100, 5148, 5220, 5580, 5700, 5796, 5850, 6468, 6660, 6732, 6900, 7260, 7308, 7350, 7380, 7524, 7644, 7650, 7700, 7740, 7812, 7956, 8460, 8550, 8700 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

Will Nicholes, Prime Signatures

Index to sequences related to prime signature

MAPLE

op(select(n->nops(factorset(n))=4 and sort([seq(op(2, a), a=ifactors(n)[2])])=[1, 1, 2, 2], [$1..8700])); # Paolo P. Lava, Jul 18 2019

MATHEMATICA

f[n_]:=Sort[Last/@FactorInteger[n]]=={1, 1, 2, 2}; Select[Range[10000], f]

PROG

(PARI) list(lim)=my(v=List(), t1, t2, t3); forprime(p=2, sqrtint(lim\60), t1=p^2; forprime(q=2, sqrtint(lim\(6*t1)), if(q==p, next); t2=q^2*t1; forprime(r=2, lim\(2*t2), if(r==p || r==q, next); t3=r*t2; forprime(s=2, lim\t3, if(s==p || s==q || s==r, next); listput(v, t3*s))))); Set(v) \\ Charles R Greathouse IV, Aug 25 2016

CROSSREFS

Part of the list A178739 .. A179696 and A030514 .. A030629, A189975 .. A189990 etc., cf. A101296. - M. F. Hasler, Jul 17 2019

Sequence in context: A144563 A175746 A291714 * A158737 A252277 A203402

Adjacent sequences:  A179687 A179688 A179689 * A179691 A179692 A179693

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Jul 24 2010

STATUS

approved

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Last modified September 16 06:48 EDT 2019. Contains 327090 sequences. (Running on oeis4.)