A179670 Numbers of the form p^3*q*r*s where p, q, r, and s are distinct primes.
840, 1320, 1560, 1848, 1890, 2040, 2184, 2280, 2760, 2856, 2970, 3080, 3192, 3432, 3480, 3510, 3640, 3720, 3864, 4158, 4440, 4488, 4590, 4760, 4872, 4914, 4920, 5016, 5130, 5160, 5208, 5250, 5304, 5320, 5640, 5720, 5928, 6072, 6210, 6216, 6360, 6426
Offset: 1
Keywords
Links
- T. D. Noe, Table of n, a(n) for n = 1..1000
- Will Nicholes, Prime Signatures
- Index to sequences related to prime signature
Programs
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Mathematica
f[n_]:=Sort[Last/@FactorInteger[n]]=={1,1,1,3}; Select[Range[10000], f] Take[#[[1]]^3 #[[2]]#[[3]]#[[4]]&/@Flatten[Permutations/@Subsets[Prime[ Range[20]],{4}],1]//Union,50] (* Harvey P. Dale, May 16 2021 *) -
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
Comments