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A047979
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Let (p1,p2), (p3,p4) be pairs of twin primes with p1*p2=p3+p4-1; sequence gives values of p4.
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4
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19, 73, 883, 2593, 180001, 206083, 388963, 2268451, 2836963, 3612673, 6329683, 6415363, 10342153, 18800713, 28486153, 32080051, 40878883, 89753203, 97050313, 127552393, 154844803, 183169801, 230953033
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OFFSET
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1,1
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LINKS
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EXAMPLE
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E.g. 5*7=17+19-1,11*13=71+73-1.
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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