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A290574
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Self numbers that are the product of two self numbers greater than one.
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1
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9, 378, 400, 525, 602, 1155, 1188, 1862, 2055, 2200, 2325, 2415, 2492, 2560, 2907, 3045, 3348, 3392, 3460, 3515, 3717, 3752, 3965, 4180, 4360, 4382, 4415, 4865, 4920, 5115, 5418, 5517, 5719, 6138, 6228, 6900, 7038, 7060, 7396, 7532, 7565, 7609, 7947, 8162, 8342, 8465, 8520, 8700, 8757, 8869, 8970, 9152, 9365, 9387, 9409, 9420, 9422, 9499, 9870, 9925
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OFFSET
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1,1
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LINKS
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EXAMPLE
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The product of the self numbers 31 and 75 is the self number 2325, so 2325 is in the sequence.
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MATHEMATICA
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Block[{nn = 10^4, s}, s = Rest@ Complement[Range@ nn, Union[Table[n + Total@ IntegerDigits@ n, {n, nn}]]]; Select[Range@ nn, Function[n, And[MemberQ[s, n], AnyTrue[Map[{#, n/#} &, Rest@ TakeWhile[Divisors@ n, # <= Sqrt@ n &]], AllTrue[#, MemberQ[s, #] &] &]]]]] (* or *)
Block[{nn = 5000, s}, s = Rest@ Complement[Range@ nn, Union@ Table[n + Total@ IntegerDigits@ n, {n, nn}]]; Select[Union@ Sort@ Map[Times @@ # &@ # &, Tuples[s, {2}]], MemberQ[s, #] &]] (* Michael De Vlieger, Aug 23 2017, after T. D. Noe at A003052 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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