Difference between prime factors of n-th semiprime is n.

[Maximilian Hasler]

unless I made some typo, the next term is
n=613668, p=5, q=613673
the following one is beyond n=6*10^6.

PARI/gp:
{ n=0; j=1; /* n=3068365-1; j=613668;*/
while( l=(j\10^4+1)*10^4, until( l < j++, until(bigomega(n+=1)==2,);
if(2!=#f=factor(n)[,1],next); if(j==f[2]-f[1],print("\n",[j,n,f])));
print1(j-1,":"n", "))}

you might also add an xref to
http://www.research.att.com/~njas/sequences/A064910
Smallest semiprime p1*p2 such that p2 mod p1 = n.

M.H.

On 9/25/07, zak seidov <zakseidov at yahoo.com> wrote:
> Neil, seqfans,
> anybody please may wish to add more terms,
> or Neil may wish to accept it as is.
> Thanks, Zak
>
> %I A000001
> %S A000001 5, 80, 86
> %N A000001 Difference between prime factors of n-th
> semiprime is n.
> %C A000001 No more terms <242556.
> %e A000001 sp(5)=14=2*7 and 7-2=5, sp(80)=249=3*83 and
> 83-3=80, sp(86)=267=3*89 and 89-3=86; sp(n)=nth
> semiprime.
> %Y A000001 A084126, A084127, A109313
> %O A000001 1
> %K A000001 ,more,nonn,
> %A A000001 Zak Seidov (zakseidov at yahoo.com), Sep 25 2007
>
>
>
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