A108215 4-almost primes equal to the product of two successive semiprimes.

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

Author

Giovanni Teofilatto, Jun 16 2005

Keywords

• easy
• nonn

Examples

			a(1) = 4*6 = 24 and a(2) = 6*9 = 54 because 4, 6 and 9 are the first three successive semiprimes.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Times@@@Partition[Select[Range[200],PrimeOmega[#]==2&],2,1], PrimeOmega[#]==4&] (* Harvey P. Dale, Nov 17 2011 *)

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

Extensions

More terms from Rick L. Shepherd, Jun 16 2005