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Search: id:A086378
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| A086378 |
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Sum of successive remainders in computing euclidean algorithm for (1,1/sqrt(n)) is rational. |
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+0
7
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| 1, 2, 4, 6, 9, 12, 16, 20, 25, 30, 36, 42, 49, 55, 56, 64, 70, 72, 81, 90, 100, 110, 121, 132, 144, 153, 155, 156, 169, 180, 182, 196, 210, 225, 240, 256, 272, 289, 305, 306, 324, 342, 361, 377, 380, 400, 420, 441, 462, 484, 504, 505, 506, 529, 546, 552, 576
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Take (a0,b0) = (1,1/sqrt(n)), then (a1,b1) = (b0,a0-b0*floor(a0/b0)), etc. and call kappa(1/sqrt(n)) = b1+b2+b3+... If kappa(1/sqrt(n)) is rational (which can be easily evaluated thanks to the periodicity of the process for a quadratic number as shown in the following MuPAD program), then n is in the sequence.
An infinity of 2nd degree polynomial functions take all their values over N in the sequence (such as x2, x2+x, 36x2+17x+2, 100x2+150x+55, 196x2+97x+12, ...).
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EXAMPLE
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7137 is in the sequence because kappa(1/sqrt(7137)) = 7/1098 (in Q).
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PROGRAM
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(MuPAD) kappa_1_over_sqrt := proc(n) local a, b, i, p; begin if (a := sqrt(n)-isqrt(n)) = 0 then return(0) end_if: i := a := simplify(1/a, sqrt); p := 1; b := 0; repeat p := simplify(p*a, sqrt); b := simplify(b*a+a-floor(a), sqrt); until (a := simplify(1/(a-floor(a)), sqrt)) = i end_repeat: return(simplify((b/(p-1) + 1/a)/sqrt(n), sqrt)); end_proc:
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CROSSREFS
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Sequence in context: A095114 A062048 A075354 this_sequence A088900 A083392 A076921
Adjacent sequences: A086375 A086376 A086377 this_sequence A086379 A086380 A086381
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KEYWORD
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nonn
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AUTHOR
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Thomas Baruchel (baruchel(AT)users.sourceforge.net), Sep 2 2003
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