A101781 Lower bound of twin primes pairs whose digital reverse is also prime.

3, 5, 11, 17, 71, 101, 107, 149, 179, 191, 311, 347, 1031, 1061, 1091, 1151, 1229, 1301, 1487, 1619, 1949, 3251, 3257, 3299, 3359, 3371, 3389, 3467, 3527, 3767, 3821, 3851, 3917, 3929, 7349, 7457, 7547, 7589, 7757, 7949, 9011, 9041, 9341, 9437, 9857, 10007

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

17 is the lower bound of twin prime pair (17,19) and its digital reverse, 71, is prime.

Mathematica

Select[Transpose[Select[Partition[Prime[Range[1500]], 2, 1], Last[#]- First[#] == 2&]][[1]], PrimeQ[FromDigits[Reverse[IntegerDigits[#]]]]&] (* Harvey P. Dale, Jun 26 2013 *)

Prog

(PARI) twlrpr(n) = { for(x=1, n, y=twinl(x); z=eval(rev(y)); if(isprime(z), print1(y", ")) ) } twinl(n) = \The n-th lower twin prime { local(c, x); c=0; x=1; while(c<n, if(isprime(prime(x)+2), c++); x++; ); return(prime(x-1)) } rev(str) = \ Get the reverse of the input string { local(tmp, s, j); tmp = Vec(Str(str)); s=""; forstep(j=length(tmp), 1, -1, s=concat(s, tmp[j])); return(s) }

Crossrefs

Sequence in context: A284306 A283399 A216181 * A101783 A078883 A355901

Adjacent sequences: A101778 A101779 A101780 * A101782 A101783 A101784

Keyword

nonn,base

Author

Cino Hilliard, Jan 26 2005

Status

approved