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A047977 Let (p1,p2), (p3,p4) be pairs of twin primes with p1*p2=p3+p4-1; sequence gives values of p2. 2
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 (list; graph; refs; listen; history; text; internal format)
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
Sequence in context: A151781 A224502 A361914 * A139403 A087820 A272032
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified July 17 20:28 EDT 2024. Contains 374377 sequences. (Running on oeis4.)