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
Links
- Robert Israel, Table of n, a(n) for n = 2..200
Programs
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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}];
Extensions
More terms from Max Alekseyev, May 03 2011