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A112421
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Number of 6 element subsets of {1,2,3,...,n} for which the sum-set has 12 elements.
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0
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2, 4, 6, 8, 10, 12, 16, 20, 24, 28, 32, 36, 42, 48, 54, 60, 66
(list; graph; refs; listen; history; internal format)
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OFFSET
| 7,1
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (2,-1,0,0,0,1,-2,1). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 26 2010]
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FORMULA
| 2x^7/((1-x)^2 (1-x^6)
a(n) = 2*A008724(n-3). a(n) = +2*a(n-1) -a(n-2) +a(n-6) -2*a(n-7) +a(n-8). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 26 2010]
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EXAMPLE
| a(7)=2 because the two sets {1 2 3 4 5 7} and (1 3 4 5 6 7} have sum-sets
{2 3 4 5 6 7 8 9 10 11 12 14} and {2 4 5 6 7 8 9 10 11 12 13 14}, respectively and each of these sum-sets has 12 elements.
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CROSSREFS
| Sequence in context: A109884 A015926 A085154 * A022483 A100180 A101814
Adjacent sequences: A112418 A112419 A112420 * A112422 A112423 A112424
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KEYWORD
| nonn
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AUTHOR
| David S Newman (DavidSNewman(AT)hotmail.com), Dec 10 2005
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