A102792 Integer part of n#/(p-7)#, where p=preceding prime to n.

105, 385, 1001, 2431, 4199, 7429, 667, 899, 1147, 1517, 65231, 82861, 2491, 3127, 3599, 4087, 4757, 347261, 5767, 6557, 7387, 97, 9797, 1009091, 1113121, 1201289, 1317919, 127, 16637, 17947, 19043, 149, 22499, 23707, 25591, 27221, 28891, 30967

Offset

7,1

Comments

0# = 1# = 2 by convention.

Links

Table of n, a(n) for n=7..44.

Formula

n# = product of primes <= n. 0#=1#=2. n#/(p-r)# is analogous to the number of permutations of n things taken r at a time: P(n, r) = n!/(n-r)! where factorial ! is replaced by primorial # and n is replaced with the preceding prime to n.

Prog

(PARI) perm(n, r) = { local(p); forprime(p=r, n, print1(floor(primorial(p)/primorial(p-r))", ") ) } 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: A195266 A113480 A190577 * A013594 A160340 A136418

Adjacent sequences: A102789 A102790 A102791 * A102793 A102794 A102795

Keyword

easy,nonn

Author

Cino Hilliard, Feb 25 2005

Status

approved