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

2, 3, 5, 7, 11, 31, 71, 101, 701, 941, 971, 991, 9001, 9011, 9221, 9521, 9941, 70001, 76001, 97001, 99401, 99431, 99571, 99989, 940001, 973001, 987101, 993401, 997811, 999431

Offset

1,1

Comments

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.

Links

Table of n, a(n) for n=1..30.

Maple

# 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);

Crossrefs

Cf. A004087, A098922, A109611.

Sequence in context: A004087 A118495 A028906 * A085300 A119388 A093487

Adjacent sequences: A118493 A118494 A118495 * A118497 A118498 A118499

Keyword

nonn,base,less

Author

Jani Melik, May 05 2006

Status

approved