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%I #28 Oct 08 2018 02:42:50
%S 1,3,6,6,8,12,12,18,16,12,18,24,24,30,24,24,36,24,36,36,24,40,48,36,
%T 36,54,48,48,54,60,48,66,48,48,60,64,72,54,60,72,72,84,72,90,72,48,72,
%U 90,96,88,90,72,108,80,108,80,108,96,72,120,108,96,126,112,120,108,96,132,120
%N Write the n-th nonprime (A018252(n)) as a product of primes; decrease one copy of the largest prime by 1 and increase one copy of the smallest prime by 1, multiply the resulting numbers.
%H Robert Israel, <a href="/A141218/b141218.txt">Table of n, a(n) for n = 1..10000</a>
%e 1st nonprime = 1 (has no prime factors); a(1) = empty product = 1.
%e 2nd nonprime = 4 = (p(max)=2)*(p(min)=2); a(2) = (2-1)*(2+1) = 1*3 = 3.
%e 3rd nonprime = 6 = (p(max)=3)*(p(min)=2); a(3) = (3-1)*(2+1) = 2*3 = 6.
%e 4th nonprime = 8 = (p(max)=2)*(p=2)*(p(min)=2); a(4) = (2-1)*2*(2+1) = 1*2*3 = 6.
%p f:= proc(m) local F,p1,p2;
%p if isprime(m) then return NULL fi;
%p F:= numtheory:-factorset(m);
%p p1:= min(F); p2:= max(F);
%p m*(p1+1)/p1*(p2-1)/p2;
%p end proc:
%p 1, seq(f(i),i=2..200); # _Robert Israel_, Oct 08 2018
%Y Cf. A018252, A141553, A141554.
%K nonn,look
%O 1,2
%A _Juri-Stepan Gerasimov_, Aug 07 2008
%E Three terms corrected by _R. J. Mathar_, Aug 18 2008
%E Entry revised by _N. J. A. Sloane_, Mar 07 2014
%E Examples revised by _Jon E. Schoenfield_, Mar 08 2014
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