A210720 Primes formed by concatenating n, n, n, n, and 1 for n = 1, 2, 3,....

33331, 99991, 242424241, 404040401, 454545451, 464646461, 494949491, 525252521, 575757571, 737373731, 787878781, 949494941, 1021021021021, 1081081081081, 1091091091091, 1211211211211, 1291291291291, 1481481481481, 1511511511511

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