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A179670 Numbers of the form p^3*q*r*s where p, q, r, and s are distinct primes. 9


%S 840,1320,1560,1848,1890,2040,2184,2280,2760,2856,2970,3080,3192,3432,

%T 3480,3510,3640,3720,3864,4158,4440,4488,4590,4760,4872,4914,4920,

%U 5016,5130,5160,5208,5250,5304,5320,5640,5720,5928,6072,6210,6216,6360,6426

%N Numbers of the form p^3*q*r*s where p, q, r, and s are distinct primes.

%C A050326(a(n)) = 7. - _Reinhard Zumkeller_, May 03 2013

%H T. D. Noe, <a href="/A179670/b179670.txt">Table of n, a(n) for n = 1..1000</a>

%H Will Nicholes, <a href="http://willnicholes.com/math/primesiglist.htm">Prime Signatures</a>

%H <a href="/index/Pri#prime_signature">Index to sequences related to prime signature</a>

%p op(select(n->nops(factorset(n))=4 and sort([seq(op(2,a),a=ifactors(n)[2])])=[1,1,1,3],[$1..6426])); # _Paolo P. Lava_, Jul 18 2019

%t f[n_]:=Sort[Last/@FactorInteger[n]]=={1,1,1,3}; Select[Range[10000], f]

%o (PARI) list(lim)=my(v=List(),t1,t2,t3); forprime(p=2,sqrtnint(lim\30, 3), t1=p^3; forprime(q=2,lim\(6*t1), if(q==p, next); t2=q*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

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Jul 23 2010

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Last modified May 28 21:37 EDT 2020. Contains 334690 sequences. (Running on oeis4.)