|
|
A085987
|
|
Product of exactly four primes, three of which are distinct (p^2*q*r).
|
|
33
|
|
|
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
|
|
|
LINKS
|
|
|
EXAMPLE
|
a(1) = 60 since 60 = 2*2*3*5 and has three distinct prime factors.
|
|
MATHEMATICA
|
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
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|