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A061208
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Numbers which can be expressed as sum of distinct triangular numbers (A000217).
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2
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1, 3, 4, 6, 7, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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These numbers were called "almost-triangular" numbers during the Peru's Selection Test for the XII IberoAmerican Olympiad (1998). All numbers >= 34 are almost-triangular: see link. [Bernard Schott, Feb 04 2013]
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LINKS
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Table of n, a(n) for n=1..71.
R. E. Woodrow, The Olympiad Corner, No. 198, Crux Mathematicorum, v25-n4(2002), 207-208, exercise 2.
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EXAMPLE
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25 = 1 + 3 + 6 + 15
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MAPLE
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gf := product(1+x^(j*(j+1)/2), j=1..100): s := series(gf, x, 200): for i from 1 to 200 do if coeff(s, x, i) > 0 then printf(`%d, `, i) fi:od:
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CROSSREFS
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Cf. A000217, A007294, A051611, A051533. Complement of A053614.
Sequence in context: A154661 A087753 A070762 * A183860 A184429 A130269
Adjacent sequences: A061205 A061206 A061207 * A061209 A061210 A061211
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 21 2001
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EXTENSIONS
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Corrected and extended by James A. Sellers, Apr 24 2001
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STATUS
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approved
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