A102788 - OEIS

A102788

Integer part of n#/((p-7)# 7#), where p=preceding prime to n.

0, 0, 0, 0, 1, 4, 11, 19, 35, 3, 4, 5, 7, 310, 394, 11, 14, 17, 19, 22, 1653, 27, 31, 35, 0, 46, 4805, 5300, 5720, 6275, 0, 79, 85, 90, 0, 107, 112, 121, 129, 137, 147, 154, 0, 175, 34581, 36029, 1, 1, 241, 55200, 57676, 265, 274, 1, 307, 321, 336, 347, 357, 370

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OFFSET

2,6

COMMENTS

0# = 1# = 2 by convention.

LINKS

Table of n, a(n) for n=2..61.

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=2, n, print1(floor(primorial(p)/primorial(p-r)/primorial(r)+.0)", ") ) } primorial(n) = \ The product of 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: A008051 A038424 A016437 * A016433 A049841 A339370

Adjacent sequences: A102785 A102786 A102787 * A102789 A102790 A102791

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Feb 25 2005

STATUS

approved