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Chen primes written backwards.
0

%I #5 Nov 21 2013 12:48:58

%S 2,3,5,7,11,31,71,91,32,92,13,73,14,74,35,95,76,17,38,98,101,701,901,

%T 311,721,131,731,931,941,751,761,971,181,191,791,991,112,722,332,932,

%U 152,752,362,962,182,392,703,113,713,733,743,353,953,973,983,104,904

%N Chen primes written backwards.

%p # 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_chen_pra:= proc(n) local i, trens, ans; trens:= [ ]; ans:=[ ]; for i from 1 to n do if (ischenprime( i ) = 'true') then ans:=[op(ans),obrni_stev(i)] fi: od: return ans end: ts_inv_chen_pra(2000);

%t psp=Take[Union[Join[Union[Times@@@Tuples[Prime[Range[100]],{2}]],Prime[Range[PrimePi[250000]]]]],200];

%t FromDigits[Reverse[IntegerDigits[#]]]&/@(Select[Prime[Range[PrimePi[1000]]],MemberQ[psp,#+2]&]) (* _Harvey P. Dale_, Feb 08 2011 *)

%Y Cf. A004087, A109611.

%K nonn,base,less

%O 1,1

%A _Jani Melik_, May 05 2006