A047977 Let (p1,p2), (p3,p4) be pairs of twin primes with p1*p2=p3+p4-1; sequence gives values of p2.

7, 13, 43, 73, 601, 643, 883, 2131, 2383, 2689, 3559, 3583, 4549, 6133, 7549, 8011, 9043, 13399, 13933, 15973, 17599, 19141, 21493, 26251, 26263, 34513, 38671, 39229, 39343, 48313, 49741, 52543, 53089, 53593, 55051, 55663, 56101

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Example

E.g. 5*7=17+19-1,11*13=71+73-1.

Prog

(PARI) list(lim)=my(v=List(), p=3, r); forprime(q=5, lim, if(q-p==2 && isprime(r=p*q\2) && isprime(r+2), listput(v, q)); p=q); Vec(v) \\ Charles R Greathouse IV, Sep 29 2015
(PARI) is(n)=isprime(n) && isprime(n-2) && isprime(n*(n-2)\2) && isprime(n*(n-2)\2+2) \\ Charles R Greathouse IV, Sep 29 2015

Crossrefs

Cf. A047976-A047979.

Sequence in context: A151781 A224502 A361914 * A139403 A087820 A272032

Adjacent sequences: A047974 A047975 A047976 * A047978 A047979 A047980

Keyword

nonn

Author

Naohiro Nomoto

Status

approved