A152034 a(n) = largest n-digit prime p whose reversal is a prime q > p.

79, 769, 9679, 98999, 995699, 9975899, 99967999, 999548999, 9999049999, 99994169999, 999989299999, 9999954799999, 99999904999999, 999999778999999, 9999999349999999, 99999994999999999, 999999971189999999, 9999999950999999999, 99999999632999999999

Offset

2,1

Links

Robert Israel, Table of n, a(n) for n = 2..200

Maple

revdigs:= proc(x) local L, i; L:= convert(x, base, 10); add(L[-i]*10^(i-1), i=1..nops(L)) end proc:
f:= proc(n)
  local d, a, B, r;
  for d from floor(n/2) by -1 do
     B:= (10^d-1)*(1+10^(n-d));
     for a from 10^(n-2*d)-1 to 1 by -1 do
       r:= revdigs(a);
       if r > a and isprime(B+10^d*a) and isprime(B+10^d*r) then return B+10^d*a fi
     od
  od
end proc:
map(f, [$2..20]); # Robert Israel, Aug 16 2016

Mathematica

Do[ p = NextPrime[10^(n ), -1 ]; Do[ p1 = FromDigits[ Reverse[IntegerDigits[p]]]; If[PrimeQ[p1] && p1 > p, Print[{n, p}]; Break[]]; p = NextPrime[p, -1], {10^9}], {n, 2, 15}];

Crossrefs

Cf. A006567, A152014, A152033.

Sequence in context: A142235 A251373 A251366 * A348894 A142816 A093279

Adjacent sequences: A152031 A152032 A152033 * A152035 A152036 A152037

Keyword

nonn,base

Author

Zak Seidov, Nov 20 2008

Extensions

More terms from Max Alekseyev, May 03 2011

Status

approved