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A230215
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Numbers divisible by 3 or 13.
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1
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3, 6, 9, 12, 13, 15, 18, 21, 24, 26, 27, 30, 33, 36, 39, 42, 45, 48, 51, 52, 54, 57, 60, 63, 65, 66, 69, 72, 75, 78, 81, 84, 87, 90, 91, 93, 96, 99, 102, 104, 105, 108, 111, 114, 117, 120, 123, 126, 129, 130, 132, 135, 138, 141, 143, 144, 147, 150, 153, 156
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OFFSET
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1,1
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COMMENTS
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In general, sequences of numbers divisible by primes p and q will have the form a(n+p+q-1) = a(n) + p*q.
The asymptotic density of this sequence is 5/13. - Amiram Eldar, Mar 25 2021
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,-1).
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FORMULA
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a(n+15) = a(n) + 39.
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MAPLE
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for n from 1 to 138 do if n mod 3 = 0 or n mod 13= 0 then print(n) fi od
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MATHEMATICA
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Select[Range[200], GCD[#, 39] > 1 &] (* T. D. Noe, Oct 15 2013 *)
With[{nn=60}, Join[3*Range[nn], 13*Floor[3/13 Range[nn]]]]//Union//Rest (* Harvey P. Dale, May 25 2020 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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