1,1

Divisible by exactly 20 primes (counted with multiplicity).

Any 20-almost prime can be represented in several ways as a product of two 10-almost primes A046314; in several ways as a product of four 5-almost primes A014614; in several ways as a product of five 4-almost primes A014613; and in several ways as a product of ten semiprimes A001358. - Jonathan Vos Post (jvospost3(AT)gmail.com), Dec 12 2004

D. W. Wilson, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Product p_i^e_i with Sum e_i = 20.

Select[Range[2*9!, 5*10! ], Plus@@Last/@FactorInteger[ # ]==20 &] [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 26 2009]

(PARI) k=20; start=2^k; finish=15000000; v=[] for(n=start, finish, if(bigomega(n)==k, v=concat(v, n))); v Depending upon the size of k and how many terms are needed, a much more efficient algorithm than the brute-force method above may be desirable. See additional comments in this section of A069280.

Cf. A001358 (semiprimes), A069272 (11-almost primes) - A069280 (19-almost primes).

Cf. A046314, A014614, A014613, A001358, A101637, A101638, A101605, A101606.

Sequence in context: A011570 A022536 A069395 this_sequence A016786 A016810 A016906

Adjacent sequences: A069278 A069279 A069280 this_sequence A069282 A069283 A069284

nonn

Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 13 2002