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A090498
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Number of divisors of all the numbers from (1/2)n(n-1)+1 to n(n+1)/2, i.e. tau(1), tau(2)+tau(3), tau(4)+tau(5)+tau(6), tau(7)+tau(8)+tau(9)+tau(10), ..., where tau(j) is the number of divisors of j.
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1
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1, 4, 9, 13, 18, 25, 31, 39, 42, 49, 61, 64, 73, 81, 92, 93, 101, 115, 120, 135, 131, 148, 157, 165, 171, 178, 195, 195, 210, 219, 229, 238, 247, 251, 273, 268, 281, 295, 308, 315, 317, 339, 340, 361, 353, 382, 381, 395, 407, 406, 427, 431, 452, 457, 469, 472
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Sequence is not increasing: a(20)=135 and a(21)=131. Difference in the number of lattice points under the curve xy= n(n+1)/2 and xy = n(n-1)/2. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 03 2005
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MAPLE
| with(numtheory): a:=n->sum(tau(j), j=n*(n-1)/2+1..n*(n+1)/2): seq(a(n), n=1..64); (Deutsch)
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CROSSREFS
| Sequence in context: A206908 A093410 A184901 * A184871 A184912 A035104
Adjacent sequences: A090495 A090496 A090497 * A090499 A090500 A090501
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Dec 04 2003
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EXTENSIONS
| Corrected and extended by Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 03 2005
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