OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
1st nonprime = 1 (has no prime factors); a(1) = empty product = 1.
2nd nonprime = 4 = (p(max)=2)*(p(min)=2); a(2) = (2-1)*(2+1) = 1*3 = 3.
3rd nonprime = 6 = (p(max)=3)*(p(min)=2); a(3) = (3-1)*(2+1) = 2*3 = 6.
4th nonprime = 8 = (p(max)=2)*(p=2)*(p(min)=2); a(4) = (2-1)*2*(2+1) = 1*2*3 = 6.
MAPLE
f:= proc(m) local F, p1, p2;
if isprime(m) then return NULL fi;
F:= numtheory:-factorset(m);
p1:= min(F); p2:= max(F);
m*(p1+1)/p1*(p2-1)/p2;
end proc:
1, seq(f(i), i=2..200); # Robert Israel, Oct 08 2018
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Juri-Stepan Gerasimov, Aug 07 2008
EXTENSIONS
Three terms corrected by R. J. Mathar, Aug 18 2008
Entry revised by N. J. A. Sloane, Mar 07 2014
Examples revised by Jon E. Schoenfield, Mar 08 2014
STATUS
approved