cp's OEIS Frontend

A118496 Reverse digits of largest Chen primes, append to sequence if result is larger Chen prime then previous one with reverse digits.

%I A118496 #2 Mar 31 2012 14:40:00
%S A118496 2,3,5,7,11,31,71,101,701,941,971,991,9001,9011,9221,9521,9941,70001,
%T A118496 76001,97001,99401,99431,99571,99989,940001,973001,987101,993401,
%U A118496 997811,999431
%N A118496 Reverse digits of largest Chen primes, append to sequence if result is larger Chen prime then previous one with reverse digits.
%C A118496 Although Chen primes are a subset of primes, this sequence is not a subset of A098922. The first number that is not member of the later is 9011.
%p A118496 # Check if number is Chen prime ischenprime:=proc(n); if (isprime(n) = 'true') then if (isprime(n+2) = 'true' or numtheory[bigomega](n+2) = 2) then return 'true' else return 'false' fi fi end: #Reverse digits 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_chen_pra:= proc(n) local i, tren, ans; tren:=0: ans:=[ ]: for i from 1 to n do if (ischenprime(i)='true' and ischenprime(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_chen_pra(200000);
%Y A118496 Cf. A004087, A098922, A109611.
%K A118496 nonn,base,less
%O A118496 1,1
%A A118496 _Jani Melik_, May 05 2006