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 A120712 Numbers n with the property that the concatenation of the proper divisors of n (i.e., excluding 1 and n) is a prime. 9
 4, 6, 9, 21, 22, 25, 33, 39, 46, 49, 51, 54, 58, 78, 82, 93, 99, 111, 115, 121, 133, 141, 142, 147, 153, 154, 159, 162, 166, 169, 174, 177, 186, 187, 189, 201, 205, 219, 226, 235, 237, 247, 249, 253, 262, 267, 274, 286, 289, 291, 294, 301, 318 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 EXAMPLE n |    divisors    | concatenation   ---+----------------+--------------    4 | (1) 2      (4) |        2    6 | (1) 2, 3   (6) |       23    9 | (1) 3      (9) |        3   21 | (1) 3, 7  (21) |       37   22 | (1) 2, 11 (22) |      211   25 | (1) 5     (25) |        5   33 | (1) 3, 11 (33) |      311   39 | (1) 3, 13 (39) |      313 MAPLE with(numtheory): for k from 2 to 1000 do: v0:=divisors(k): nn:=nops(v0): if nn > 2 then v1:=[seq(v0[j], j=2..nn-1)]: v2:=cat(seq(convert(v1[n], string), n=1..nops(v1))): v3:=parse(v2): if isprime(v3) = true then lprint(k, v3) fi: fi: od: # Simon Plouffe MATHEMATICA fQ[n_] := PrimeQ@ FromDigits@ Most@ Rest@ Divisors@ n; Select[ Range[2, 320], fQ] CROSSREFS Cf. A037274, A037278, A037279, A106708, A120713, A120716. Cf. A130139, A130140, A130141, A130142. Sequence in context: A171127 A098485 A293399 * A115698 A039566 A032817 Adjacent sequences:  A120709 A120710 A120711 * A120713 A120714 A120715 KEYWORD nonn,base AUTHOR Eric Angelini, Jul 19 2007 STATUS approved

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Last modified May 22 11:15 EDT 2022. Contains 353949 sequences. (Running on oeis4.)