

A141218


Write the nth 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.


6



1, 3, 6, 6, 8, 12, 12, 18, 16, 12, 18, 24, 24, 30, 24, 24, 36, 24, 36, 36, 24, 40, 48, 36, 36, 54, 48, 48, 54, 60, 48, 66, 48, 48, 60, 64, 72, 54, 60, 72, 72, 84, 72, 90, 72, 48, 72, 90, 96, 88, 90, 72, 108, 80, 108, 80, 108, 96, 72, 120, 108, 96, 126, 112, 120, 108, 96, 132, 120
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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) = (21)*(2+1) = 1*3 = 3.
3rd nonprime = 6 = (p(max)=3)*(p(min)=2); a(3) = (31)*(2+1) = 2*3 = 6.
4th nonprime = 8 = (p(max)=2)*(p=2)*(p(min)=2); a(4) = (21)*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*(p21)/p2;
end proc:
1, seq(f(i), i=2..200); # Robert Israel, Oct 08 2018


CROSSREFS

Cf. A018252, A141553, A141554.
Sequence in context: A178746 A229986 A025500 * A342425 A318845 A147866
Adjacent sequences: A141215 A141216 A141217 * A141219 A141220 A141221


KEYWORD

nonn,look


AUTHOR

JuriStepan 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



