%I #13 Oct 22 2022 14:12:36

%S 43,53,97,107,1613,2423,3331,3631,4241,4643,5147,5347,5653,5953,6361,

%T 6661,6761,6967,7573,7673,7873,8179,8783,9689,102101,106103,108107,

%U 111109,114113,116113,123113,125113,129127,130127,135131,137131,144139,145139,147139,148139

%N Primes formed from the concatenation of n and previousprime(n).

%H K. D. Bajpai, <a href="/A280388/b280388.txt">Table of n, a(n) for n = 1..9135</a>

%e 43 is in the sequence because it is prime formed from the concatenation of 4 and 3, where 3 is largest prime < 4.

%e 1613 is in the sequence because it is prime formed from the concatenation of 16 and 13, where 13 is largest prime < 16.

%p with(numtheory): select( isprime,[seq((n*10^floor(evalf(log10(prevprime(n))+1, 100))+prevprime(n)), n=3..500)]);

%p P:=proc(i) local a, n, c; c:=1; for n from 3 by 1 to i do a:=n*10^floor(evalf(log10(prevprime(n))+1, 100))+prevprime(n);if (isprime(a)) then lprint(c,a);c:=c+1; fi;od; end: P(10000);

%t Select[Table[FromDigits[Join[IntegerDigits[n],IntegerDigits[NextPrime[n,-1]]]],{n,200}],PrimeQ] (* _Harvey P. Dale_, Oct 22 2022 *)

%Y Cf. A000040, A084667, A084669, A151799, A151800.

%K nonn,base

%O 1,1

%A _K. D. Bajpai_, Jan 01 2017