A128550 a(n) = p, the lesser of twin primes (p, q=p+2) such that p*q + p + q is prime.
3, 5, 11, 17, 41, 59, 101, 137, 311, 419, 521, 809, 1019, 1049, 1151, 1229, 1319, 1427, 2111, 2237, 2267, 3119, 3329, 3371, 3539, 4001, 4049, 4091, 4217, 4421, 4721, 5009, 6359, 6569, 6689, 6761, 7487, 7949, 8537, 8627, 9629, 9719, 10007, 10091, 10709
Offset: 1
Keywords
Examples
3, 5 and 3*5+3+5=23 are prime; 5, 7 and 5*7+5+7=47 are prime; 11, 13 and 11*13+11+13 are primes.
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
lst={};Do[p=Prime[n];r=p+2;If[PrimeQ[r],If[PrimeQ[p*r+p+r],AppendTo[lst,p]]],{n,8!}];lst (* Vladimir Joseph Stephan Orlovsky, Nov 28 2009 *) Transpose[Select[Select[Partition[Prime[Range[1500]],2,1],#[[2]]- #[[1]] == 2&],PrimeQ[Times@@#+Total[#]]&]][[1]] (* Harvey P. Dale, Aug 24 2014 *) -
PARI
is(n)=isprime(n)&&isprime(n+2)&&isprime(n^2+4*n+2) \\ Charles R Greathouse IV, Jan 29 2013
Comments