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%I #5 Oct 01 2013 17:58:07
%S 0,2,5,1,23,2,53,3,4,149,6,6,293,7,8,9,599,11,11,863,13,13,14,16,16,
%T 1733,17,1943,18,21,21,22,3173,24,3749,26,27,27,28,29,5399,31,6143,32,
%U 6533,35,37,37,8663,38,39,9599,41,42,43,44,12149,46,46,13253,48
%N Integer part of n#/((p-3)# 3#), where p=preceding prime to n.
%C 0# = 1# = 2 by convention.
%F n# = product of primes <= n. 0#=1#=2. n#/((p-r)# r#) is analogous to the number of combinations of n things taken r at a time: C(n, r) = n!/((n-r)! r!) where factorial ! is replaced by primorial # and n is replaced with the preceding prime to n.
%o (PARI) c(n,r) = { local(p); forprime(p=r,n, print1(floor(primorial(p)/primorial(p-r)/primorial(r)+.0)",") ) } primorial(n) = \ The product primes <= n using the pari primelimit. { local(p1,x); if(n==0||n==1,return(2)); p1=1; forprime(x=2,n,p1*=x); return(p1) }
%K easy,nonn
%O 2,2
%A _Cino Hilliard_, Feb 25 2005
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