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

1,1

Comments

All entries are in A001358.

Links

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

Formula

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

Example

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.

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

Crossrefs

Cf. A014612, A162361.

Sequence in context: A159475 A098350 A276269 * A058640 A075653 A075656

Adjacent sequences: A163170 A163171 A163172 * A163174 A163175 A163176

Keyword

nonn,look

Author

Juri-Stepan Gerasimov, Jul 22 2009

Extensions

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

Status

approved