A131284 Numbers n such that difference between prime factors of n-th semiprime is n.

5, 80, 86, 613668, 6384425704

Offset

1,1

Comments

The 6384425704th semiprime is 44690979977 = 7*6384425711. 6384425711 - 7 = 6384425704. - Donovan Johnson, Jul 11 2010

Links

Table of n, a(n) for n=1..5.

Example

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) = n-th semiprime.

Prog

(PARI)
{ 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", "))} \\ M. F. Hasler, Sep 28 2007

Crossrefs

Cf. A064910, A084126, A084127, A109313.

Sequence in context: A134531 A347841 A062250 * A105917 A269792 A144344

Adjacent sequences: A131281 A131282 A131283 * A131285 A131286 A131287

Keyword

more,nonn

Author

Zak Seidov, Sep 25 2007

Extensions

a(4) = 613668 (p=5, q=613673) from M. F. Hasler, Sep 28 2007

a(5) from Donovan Johnson, Jul 11 2010

Status

approved