%I #4 Mar 31 2012 14:40:00
%S 2,3,5,7,11,31,71,73,97,101,701,941,971,991,9001,9601,9721,9931,9941,
%T 9967,70001,90001,93001,96001,97001,99401,99611,99721,99881,99923,
%U 99989,940001,972001,973001,996001,997001,999101,999331,999431,999631,999931
%N Reverse digits of largest primes, append to sequence if result is larger prime then previous one with reverse digits.
%e The prime 37 in reverse is 73. 73 is prime and is larger than previous prime (17), written with reverse digits 71.
%p obrni_stev:=proc(n) local i, tren, tren1, st, ans; ans:=[ ]: tren:=n: tren1:=0: for i while (tren>0) do st:=round( 10*frac(tren/10) ): ans:=[ op(ans), st ]: tren:=trunc(tren/10): od; for i from 0 to nops(ans)-1 do tren1:= tren1 + op(nops(ans)-i, ans)*10^(i); od: RETURN(tren1); end: ts_inv_prav_pra:= proc(n) local i, tren, ans; tren:=0: ans:=[ ]: for i from 1 to n do if ( isprime( i ) = 'true' and isprime( obrni_stev (i) )='true' and obrni_stev(i) > tren ) then ans:=[ op(ans),obrni_stev(i) ]; tren:=obrni_stev(i); fi: od: RETURN(ans); end: ts_inv_prav_pra(200000);
%Y Cf. A004087, A095180.
%K base,easy,nonn
%O 1,1
%A _Jani Melik_, Oct 18 2004