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Primes p such that the largest digit of the concatenation of p and the p-th prime is either 1 or 9.
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%I #20 Feb 08 2022 13:17:53

%S 17,19,29,41,43,59,79,89,97,109,127,131,139,149,157,163,167,179,191,

%T 193,197,199,211,223,229,239,251,263,269,293,317,337,349,359,373,379,

%U 389,397,401,409,419,421,433,439,443,449,457,461,463,467,479,487,491,499

%N Primes p such that the largest digit of the concatenation of p and the p-th prime is either 1 or 9.

%H Harvey P. Dale, <a href="/A155089/b155089.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Prime[Range[250]],MemberQ[{1,9},Max[Join[IntegerDigits[ #],IntegerDigits[ Prime[#]]]]]&] (* _Harvey P. Dale_, Feb 08 2022 *)

%o (PARI) isok(p) = isprime(p) && (vecmax(digits(eval(concat(Str(p), Str(prime(p)))))) == 9); \\ _Michel Marcus_, Feb 18 2021

%Y Cf. A000040.

%K nonn,base,less

%O 1,1

%A _Juri-Stepan Gerasimov_, Jan 20 2009

%E Entries checked by _R. J. Mathar_, May 10 2010