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Search: id:A124080
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| A124080 |
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10 times triangular numbers. |
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+0
6
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| 0, 10, 30, 60, 100, 150, 210, 280, 360, 450, 550, 660, 780, 910, 1050, 1200, 1360, 1530, 1710, 1900, 2100, 2310, 2530, 2760, 3000, 3250, 3510, 3780, 4060, 4350, 4650, 4960, 5280, 5610, 5950, 6300, 6660, 7030, 7410, 7800, 8200, 8610, 9030, 9460, 9900, 10350
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OFFSET
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0,2
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COMMENT
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If Y is a 5-subset of an n-set X then, for n>=5, a(n-4) is equal to the number of 5-subsets of X having exactly three elements in common with Y. Y is a 5-subset of an n-set X then, for n>=6, a(n-6) is the number of (n-5)-subsets of X having exactly two elements in common with Y.lso, if - Milan R. Janjic (agnus(AT)blic.net), Dec 28 2007
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FORMULA
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a(n)=10*C(n,2), n>=1
a(n)=A049598-A002378. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 06 2007
a(n)=n*(n+1)*5, n>=0 . - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 06 2007
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MAPLE
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[seq(10*binomial(n, 2), n=1..51)];
seq(n*(n+1)*5, n=0..39); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 06 2007
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CROSSREFS
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Cf. A028895, A046092, A045943, A002378, A028896, A024966, A033996, A027468.
Cf. A002378, A049598.
Sequence in context: A096844 A031299 A104044 this_sequence A034127 A005052 A057344
Adjacent sequences: A124077 A124078 A124079 this_sequence A124081 A124082 A124083
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KEYWORD
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easy,nonn
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AUTHOR
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Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 24 2006
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