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Date: 12-2-2020
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Date: 3-10-2020
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Date: 30-5-2020
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The Engel expansion, also called the Egyptian product, of a positive real number is the unique increasing sequence
of positive integers
such that
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The following table gives the Engel expansions of Catalan's constant, e, the Euler-Mascheroni constant ,
, and the golden ratio
.
constant | OEIS | Engel expansion |
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A028254 | 1, 3, 5, 5, 16, 18, 78, 102, 120, ... |
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A028257 | 1, 2, 3, 3, 6, 17, 23, 25, 27, 73, ... |
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A118239 | 1, 2, 12, 30, 56, 90, 132, 182, ... |
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A000027 | 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, ... |
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A059193 | 3, 10, 28, 54, 88, 130, 180, 238, 304, 378, ... |
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A053977 | 2, 7, 13, 19, 85, 2601, 9602, 46268, 4812284, ... |
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A054543 | 2, 2, 2, 4, 4, 5, 5, 12, 13, 41, 110, ... |
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A059180 | 2, 3, 7, 9, 104, 510, 1413, 2386, ... |
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A028259 | 1, 2, 5, 6, 13, 16, 16, 38, 48, 58, 104, ... |
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A006784 | 1, 1, 1, 8, 8, 17, 19, 300, 1991, 2492, ... |
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A014012 | 4, 4, 11, 45, 70, 1111, 4423, 5478, 49340, ... |
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A068377 | 1, 6, 20, 42, 72, 110, 156, 210, ... |
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A118326 | 2, 2, 22, 50, 70, 29091, 49606, 174594, ... |
has a very regular Engel expansion, namely 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, ... (OEIS A000027). Interestingly, the expansion for the hyperbolic sine
has closed form
for
, which means the expansion for the hyperbolic cosine
has the closed form
for
. Similarly, the Engel expansion for
is
for
, which follows from
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REFERENCES:
Engel, F. "Entwicklung der Zahlen nach Stammbruechen." Verhandlungen der 52. Versammlung deutscher Philologen und Schulmaenner in Marburg. pp. 190-191, 1913.
Erdős, P. and Shallit, J. O. "New Bounds on the Length of Finite Pierce and Engel Series." Sem. Theor. Nombres Bordeaux 3, 43-53, 1991.
Finch, S. R. Mathematical Constants. Cambridge, England: Cambridge University Press, pp. 53-59, 2003.
Schweiger, F. Ergodic Theory of Fibred Systems and Metric Number Theory. Oxford, England: Oxford University Press, 1995.
Sloane, N. J. A. Sequences A000027/M0472, A006784/M4475, A014012, A028254, A028257, A028259, A053977, A054543, A059180, A059193, A068377, A118239, and A118326 in "The On-Line Encyclopedia of Integer Sequences."
Wu, J. "How Many Points Have the Same Engel and Sylvester Expansions?." J. Number Th. 103, 16-26, 2003.
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