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Prime numbers n such that replacing each digit d in the decimal expansion of n with its 9's complement produces a prime.
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%I #13 Sep 13 2017 02:16:21

%S 2,7,97,997,99999999999999997

%N Prime numbers n such that replacing each digit d in the decimal expansion of n with its 9's complement produces a prime.

%C a(n) = {2} union {primes of the form 10^n - 3} = {2} union {A093172}.

%C Primes p such that A061601(p) is also prime.

%C The next term has 140 digits.

%e 997 is in the sequence because 997 becomes (002) = 2, which is prime.

%t lst={};f[n_]:=Block[{a=IntegerDigits[Prime[n]],b="",k=1,l},l=Length[a];While[k<l+1,b=StringJoin[b,ToString[9-a[[k]]]];k++];ToExpression[b]];Do[If[PrimeQ[f[n]],AppendTo[lst, Prime[n]]],{n,1,10^6}];lst

%Y Cf. A093172, A173833.

%K nonn,base

%O 1,1

%A _Michel Lagneau_, Apr 10 2014