A171807 - OEIS

%I #8 Nov 21 2013 12:49:59

%S 37,71,157,167,199,907,953,971,991,1151,1193,1213,1223,1231,1237,1279,

%T 1283,1381,1429,1471,1499,1523,1583,1597,1601,1619,1669,1811,1831,

%U 1867,3299,3343,3347,3371,3373,3391,3463,3467,3469,3527,3541,3719,3767,3803

%N Emirps (A006567) p such that R(prime(p)) is prime.

%F {n such that n is in A000040 and A006567(n) is in A000040 and A000040(n) is in A000040 and A006567(A000040(n)) is in A000040}.

%e a(1) = 37 because 37 and R(37) = 73 are prime, as are prime(37) = 157 and R(prime(37)) = 751. a(2) = 71 because 71 and R(71) = 17 are prime, as are prime(71) = R(prime(71)) = 353 (which is not an emirp because the reversal is the same prime). a(3) = 157 because 157 and R(157) = 751 are prime, as are prime(157) = R(prime(157)) = 919 (which is not an emirp because the reversal is the same prime). a(4) = 167 because 167 and R(157) = 671 are prime, as are prime(167) = 991 and R(prime(167)) = 199. a(5) = 199 because 199 and (199) = 991 are prime, as are prime(199) = 1217 and R(1217)= prime(912) = 7121.

%t emQ[n_]:=Module[{idn=IntegerDigits[n],revidn},revidn=Reverse[idn];idn!= revidn && PrimeQ[FromDigits[revidn]] && PrimeQ[FromDigits[ Reverse[ IntegerDigits[ Prime[n]]]]]]; Select[Prime[Range[600]],emQ] (* _Harvey P. Dale_, Mar 01 2012 *)

%Y Cf. A000040, A004086, A006567.

%K easy,nonn,less,base

%O 1,1

%A _Jonathan Vos Post_, Dec 18 2009

%E More terms from _R. J. Mathar_, Jan 25 2010