The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A085987 Product of exactly four primes, three of which are distinct (p^2*q*r). 30
 60, 84, 90, 126, 132, 140, 150, 156, 198, 204, 220, 228, 234, 260, 276, 294, 306, 308, 315, 340, 342, 348, 350, 364, 372, 380, 414, 444, 460, 476, 490, 492, 495, 516, 522, 525, 532, 550, 558, 564, 572, 580, 585, 620, 636, 644, 650, 666, 693, 708, 726 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A014613 is completely determined by A030514, A065036, A085986, A085987 and A046386 since p(4) = 5. (cf. A000041). More generally, the first term of sequences which completely determine the k-almost primes can be found in A036035 (a resorted version of A025487). A050326(a(n)) = 4. - Reinhard Zumkeller, May 03 2013 LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 EXAMPLE a(1) = 60 since 60 = 2*2*3*5 and has three distinct prime factors. MAPLE op(select(n->nops(factorset(n))=3 and sort([seq(op(2, a), a=ifactors(n)[2])])=[1, 1, 2], [\$1..726])); # Paolo P. Lava, Jul 18 2019 MATHEMATICA f[n_]:=Sort[Last/@FactorInteger[n]]=={1, 1, 2}; Select[Range[2000], f] (* Vladimir Joseph Stephan Orlovsky, May 03 2011 *) pefp[{a_, b_, c_}]:={a^2 b c, a b^2 c, a b c^2}; Module[{upto=800}, Select[ Flatten[ pefp/@Subsets[Prime[Range[PrimePi[upto/6]]], {3}]]//Union, #<= upto&]] (* Harvey P. Dale, Oct 02 2018 *) PROG (PARI) list(lim)=my(v=List(), t, x, y, z); forprime(p=2, lim^(1/4), t=lim\p^2; forprime(q=p+1, sqrtint(t), forprime(r=q+1, t\q, x=p^2*q*r; y=p*q^2*r; listput(v, x); if(y<=lim, listput(v, y); z=p*q*r^2; if(z<=lim, listput(v, z)))))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 15 2011 (PARI) is(n)=vecsort(factor(n)[, 2]~)==[1, 1, 2] \\ Charles R Greathouse IV, Oct 19 2015 CROSSREFS Cf. A001248, A006881, A030078, A054753, A007304, A050997, A046387, A036035, A086974. Subsequence of A014613, A307341, A178212. Sequence in context: A350371 A009129 A174292 * A356413 A086974 A099831 Adjacent sequences: A085984 A085985 A085986 * A085988 A085989 A085990 KEYWORD nonn AUTHOR Alford Arnold, Jul 08 2003 EXTENSIONS More terms from Reinhard Zumkeller, Jul 25 2003 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 7 22:02 EST 2022. Contains 358671 sequences. (Running on oeis4.)