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A131284 Numbers n such that difference between prime factors of n-th semiprime is n. 3
5, 80, 86, 613668, 6384425704 (list; graph; refs; listen; history; text; internal format)
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: A141828 A134531 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

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Last modified February 22 07:53 EST 2018. Contains 299447 sequences. (Running on oeis4.)