# [seqfan] Re: A170817, A170818 xref suggested

Maximilian Hasler maximilian.hasler at gmail.com
Wed Dec 23 21:27:56 CET 2009

```On Wed, Dec 23, 2009 at 4:12 PM, Alois Heinz <heinz at hs-heilbronn.de> wrote:
> Jonathan Post schrieb:
>> A170818
>> A170817

I suggest rephrasing the "all" in

A170818  	 	 a(n) = product of all primes of form 4k+1 that divide n.

(what is meant is "with multiplicity") -
What are "all primes =1[4] dividing  25" ?
5 and 5 ?
(*frown*)

and for completeness there should also be the =3[4] equivalent:

%o A000001 (PARI)
for(n=1,99, t=select(x->x%4==3, factor(n)[,1]); print1(prod(i=1,#t,t[i])","))

%N A000001 product of (distinct) primes of the form 4k-1 that divide n

%S A000001
1,1,3,1,1,3,7,1,3,1,11,3,1,7,3,1,1,3,19,1,21,11,23,3,1,1,3,7,1,3,31,1,33,1,7,3,
1,19,3,1,1,21,43,11,3,23,47,3,7,1,3,1,1,3,11,7,57,1,59,3,1,31,21,1,1,33,67,1,
69,7,71,3,1,1,3,19,77,3,79,1,3,1,83,21,1,43,3,11,1,3,7,23,93,47,19,3,1,7,33,1,
1,3,103,1,21,1,107,3,1,11,3,7,1,57,23,1,3,59,7,3,11,1,3,

Maximilian

```