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%I #17 Aug 16 2024 17:14:07
%S 23,34,35,56,57,78,79,710,711,1112,1113,1314,1315,1316,1317,1718,1719,
%T 1920,1921,1922,1923,2324,2325,2326,2327,2328,2329,2930,2931,3132,
%U 3133,3134,3135,3136,3137,3738,3739,3740,3741,4142,4143,4344
%N Concatenate prevprime(n) and n.
%H Harvey P. Dale, <a href="/A049851/b049851.txt">Table of n, a(n) for n = 3..1000</a>
%t Table[NextPrime[n,-1]*10^IntegerLength[n]+n,{n,3,50}] (* _Harvey P. Dale_, Aug 16 2024 *)
%o (PARI) a(n) = eval(concat(Str(precprime(n-1)), Str(n))); \\ _Michel Marcus_, Aug 11 2017
%Y Cf. A151799.
%K nonn,base
%O 3,1
%A _N. J. A. Sloane_