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 A210720 Primes formed by concatenating n, n, n, n, and 1 for n = 1, 2, 3,.... 2
 33331, 99991, 242424241, 404040401, 454545451, 464646461, 494949491, 525252521, 575757571, 737373731, 787878781, 949494941, 1021021021021, 1081081081081, 1091091091091, 1211211211211, 1291291291291, 1481481481481, 1511511511511 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This is to four (duplicated strings concatenated) as A210712 is to three (duplicated strings concatenated, and as A210511 is to two (duplicated strings concatenated). LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 EXAMPLE a(1) = 33331 because Concat(3,3,3,1) = 3331 which is in A000040. MAPLE A210720 := proc(n)         local p;         [n, n, n, n, 1] ;         p := digcatL(%) ;         if isprime(p) then                 printf("%d, ", p) ;         end if; end proc: for n from 1 to 400 do         A210720(n) ; end do: # R. J. Mathar, Feb 10 2013 MATHEMATICA Select[Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[1], {}}]], {n, 200}], PrimeQ] (* Vincenzo Librandi, Mar 15 2013 *) Select[Table[FromDigits[Join[Flatten[IntegerDigits/@PadRight[{}, 4, n]], {1}]], {n, 200}], PrimeQ] (* Harvey P. Dale, Oct 16 2017 *) PROG (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 CROSSREFS Cf. A210511, A210712. Sequence in context: A043628 A205410 A337953 * A233751 A205212 A206220 Adjacent sequences:  A210717 A210718 A210719 * A210721 A210722 A210723 KEYWORD nonn,base,easy AUTHOR Jonathan Vos Post, Jan 29 2013 STATUS approved

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Last modified May 17 09:20 EDT 2022. Contains 353741 sequences. (Running on oeis4.)