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A102786 Integer part of n#/((p-3)# 3#), where p=preceding prime to n. 0
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, 1733, 17, 1943, 18, 21, 21, 22, 3173, 24, 3749, 26, 27, 27, 28, 29, 5399, 31, 6143, 32, 6533, 35, 37, 37, 8663, 38, 39, 9599, 41, 42, 43, 44, 12149, 46, 46, 13253, 48 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

0# = 1# = 2 by convention.

LINKS

Table of n, a(n) for n=2..62.

FORMULA

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.

PROG

(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) }

CROSSREFS

Sequence in context: A047921 A242783 A177250 * A222637 A190950 A159985

Adjacent sequences:  A102783 A102784 A102785 * A102787 A102788 A102789

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Feb 25 2005

STATUS

approved

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Last modified November 13 12:45 EST 2019. Contains 329094 sequences. (Running on oeis4.)