A007774 : k,d-almost primes?

[zak seidov]

Dear seqfan gurus,

My Q is about %C: 
 what is k and what is d? 
 k-almost primess are different from 
 d-almost primes?

I humbly suggest that there's some confusion...

Thanks, Zak

I A007774
%S A007774
6,10,12,14,15,18,20,21,22,24,26,28,33,34,35,36,38%N
A007774 Divisible by exactly 2 different primes.
%C A007774 The smallest number with two distinct prime
divisors is the product of first two 
               primes, 2*3=6. Note that in A001358
(product of two primes), A014612 
               (product of three primes), A014613
(product of four primes), A014614 
               (product of five primes), primes are
not necessarily distinct, so 
               k-almost primes are a more general
class. In the sequence, d-almost 
               primes with d=2 are considered, see
also A074969 (d=6), A051270 (d=5), 
               A033993 (d=4), A033992 (d=3). The case
d=1 (or k=1) corresponds to 
               primes A000040.
%F A007774 omega(a(n)) = A001221(a(n)) = 2. - Jonathan
Vos Post (jvospost2(AT)yahoo.com), Sep 
               20 2005
%e A007774 20 is OK because 20=2^2*5 with two distinct
prime divisors 2, 5.
%p A007774 with(numtheory,factorset):f := proc(n) if
nops(factorset(n))=2 then RETURN(n) fi; 
               end;%A A007774
ltp1000(AT)hermes.cam.ac.uk



 
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