A163173 The n-th product of three primes divided by its central prime factor.

4, 6, 6, 10, 9, 14, 10, 14, 22, 15, 10, 26, 21, 22, 34, 14, 15, 38, 26, 46, 14, 33, 34, 21, 22, 38, 58, 39, 62, 25, 26, 46, 21, 74, 51, 22, 82, 33, 34, 57, 86, 58, 35, 26, 62, 94, 38, 39, 69, 106, 74, 46, 33, 118, 34, 22, 122, 35, 82, 51, 86, 87, 38, 134, 39, 55, 93, 94, 142, 57, 26

Offset: 1

Author

Juri-Stepan Gerasimov, Jul 22 2009

Keywords

• nonn
• look

Comments

All entries are in A001358.

Examples

			a(1)=2*2*2/2=4. a(2)=2*2*3/2=6. a(3)=2*3*3/3=6. a(4)=2*2*5/2=10. a(5)=3*3*3/3 = 9.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A014612, A162361.

Programs

Maple

f:= proc(n) local P;
   if numtheory:-bigomega(n) <> 3 then return NULL fi;
   P:= numtheory:-factorset(n);
   min(P)*max(P)
end proc:
map(f, [$1..500]); # Robert Israel, Jun 05 2023

Formula

a(n) = A014612(n)/A162361(n).

Extensions

a(57) corrected by R. J. Mathar, Jul 25 2009