A047979 Let (p1,p2), (p3,p4) be pairs of twin primes with p1*p2=p3+p4-1; sequence gives values of p4.

19, 73, 883, 2593, 180001, 206083, 388963, 2268451, 2836963, 3612673, 6329683, 6415363, 10342153, 18800713, 28486153, 32080051, 40878883, 89753203, 97050313, 127552393, 154844803, 183169801, 230953033

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, sqrtint(lim\1*2-2)+1, if(q-p==2 && isprime(r=p*q\2) && isprime(r+2), listput(v, r+2)); p=q); Vec(v) \\ Charles R Greathouse IV, Sep 29 2015
(PARI) is(n)=my(p=sqrtint(2*n-3)); p*(p+2)==2*n-3 && isprime(n) && isprime(n-2) && isprime(p) && isprime(p+2) \\ Charles R Greathouse IV, Sep 29 2015

Crossrefs

Cf. A047976-A047978.

Sequence in context: A220447 A294460 A118593 * A290241 A159997 A073566

Adjacent sequences: A047976 A047977 A047978 * A047980 A047981 A047982

Keyword

nonn

Author

Naohiro Nomoto

Status

approved