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A108215
4-almost primes equal to the product of two successive semiprimes.
2
24, 54, 90, 140, 210, 315, 462, 550, 650, 858, 1122, 1190, 1330, 1482, 1794, 2254, 2499, 2805, 3135, 3306, 3596, 4030, 4485, 5106, 5698, 6314, 6970, 7310, 7482, 7917, 8463, 8742, 8930, 10070, 11766, 12765, 13570, 14042, 14399, 14762, 15006, 15867
OFFSET
1,1
LINKS
EXAMPLE
a(1) = 4*6 = 24 and a(2) = 6*9 = 54 because 4, 6 and 9 are the first three successive semiprimes.
MATHEMATICA
Select[Times@@@Partition[Select[Range[200], PrimeOmega[#]==2&], 2, 1], PrimeOmega[#]==4&] (* Harvey P. Dale, Nov 17 2011 *)
PROG
(PARI) sp=4; for(sq=6, 300, if(bigomega(sq)==2, print1(sp*sq, ", "); sp=sq)) \\ Rick L. Shepherd
(PARI) list(lim)=my(v=List(), s=sqrtint(lim\1), u=v); forprime(p=2, s\2, forprime(q=2, min(p, s\p), listput(v, p*q))); v=Set(v); for(i=2, #v, listput(u, v[i-1]*v[i])); for(k=s+1, lim\v[#v], if(bigomega(k)==2, listput(u, v[#v]*k); break)); Set(u) \\ Charles R Greathouse IV, Feb 02 2017
CROSSREFS
Sequence in context: A259023 A301575 A294156 * A322609 A234238 A228876
KEYWORD
easy,nonn
AUTHOR
Giovanni Teofilatto, Jun 16 2005
EXTENSIONS
More terms from Rick L. Shepherd, Jun 16 2005
STATUS
approved