A112785 Members of twin prime pairs using only digits 7 and 9.

79997, 79999, 777977, 777979, 7977797, 7977799, 77997779, 77997977, 77997979, 99777779, 799999799, 977797979, 977999777, 977999779, 979797779, 999799979, 7777997999, 7797799979, 7979997797, 7979997799, 7999777997, 7999777999, 7999797977, 7999797979

Offset

1,1

Links

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

Mathematica

Select[Flatten[Table[FromDigits/@Tuples[{7, 9}, n], {n, 2, 11}]], PrimeQ[#] && Or@@PrimeQ[#+{2, -2}]&] (* Harvey P. Dale, Nov 06 2013 *)

Prog

(PARI) istwin(n)=ispseudoprime(n)&&ispseudoprime(if(n%3==1, n-2, n+2))
do(D)=my(v=List(), t); for(d=5, D, for(i=0, 2^d-1, t=sum(j=0, d-1, if(bittest(i, j), 9, 7)*10^j); if(istwin(t), listput(v, t)))); Vec(v)
\\ Charles R Greathouse IV, Nov 06 2013

Crossrefs

Sequence in context: A185473 A235075 A229700 * A106775 A258951 A234756

Adjacent sequences: A112782 A112783 A112784 * A112786 A112787 A112788

Keyword

base,nonn

Author

Amarnath Murthy, Jan 02 2006

Extensions

Edited and extended by D. S. McNeil, Nov 27 2010

Corrected and extended by Harvey P. Dale, Nov 06 2013

Status

approved