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A120712
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Numbers n with property that the concatenation of the proper divisors of n (i.e. excluding 1 and n) is a prime.
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9
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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
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OFFSET
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1,1
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COMMENTS
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Numbers n with property that the concatenation of all proper divisors of n excluding 1 is a prime. [From Lekraj Beedassy, Jun 15 2009]
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1000
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EXAMPLE
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n -> divisors -> prime
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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
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MAPLE
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Maple program from Simon Plouffe: 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:
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MATHEMATICA
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fQ[n_] := PrimeQ@ FromDigits@ Most@ Rest@ Divisors@ n; Select[ Range[2, 320], fQ]
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CROSSREFS
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Cf. A120716, A120713, A037274, A037278, A106708, A037279.
Cf. A130139, A130140, A130141, A130142.
Sequence in context: A152002 A171127 A098485 * A115698 A039566 A032817
Adjacent sequences: A120709 A120710 A120711 * A120713 A120714 A120715
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KEYWORD
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nonn,base,changed
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AUTHOR
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Eric Angelini, Jul 19 2007
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STATUS
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approved
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