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%I #28 Sep 08 2022 08:46:01
%S 33331,99991,242424241,404040401,454545451,464646461,494949491,
%T 525252521,575757571,737373731,787878781,949494941,1021021021021,
%U 1081081081081,1091091091091,1211211211211,1291291291291,1481481481481,1511511511511
%N Primes formed by concatenating n, n, n, n, and 1 for n = 1, 2, 3,....
%C This is to four (duplicated strings concatenated) as A210712 is to three (duplicated strings concatenated, and as A210511 is to two (duplicated strings concatenated).
%H Vincenzo Librandi, <a href="/A210720/b210720.txt">Table of n, a(n) for n = 1..1000</a>
%e a(1) = 33331 because Concat(3,3,3,1) = 3331 which is in A000040.
%p A210720 := proc(n)
%p local p;
%p [n,n,n,n,1] ;
%p p := digcatL(%) ;
%p if isprime(p) then
%p printf("%d,",p) ;
%p end if;
%p end proc:
%p for n from 1 to 400 do
%p A210720(n) ;
%p end do: # _R. J. Mathar_, Feb 10 2013
%t Select[Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[1], {}}]], {n, 200}], PrimeQ] (* _Vincenzo Librandi_, Mar 15 2013 *)
%t Select[Table[FromDigits[Join[Flatten[IntegerDigits/@PadRight[{},4,n]],{1}]],{n,200}],PrimeQ] (* _Harvey P. Dale_, Oct 16 2017 *)
%o (Magma) [nnnn1: n in [1..200] | IsPrime(nnnn1) where nnnn1 is Seqint([1] cat Intseq(n) cat Intseq(n) cat Intseq(n) cat Intseq(n))]; // _Vincenzo Librandi_, Mar 15 2013
%Y Cf. A210511, A210712.
%K nonn,base,easy
%O 1,1
%A _Jonathan Vos Post_, Jan 29 2013
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