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A076307
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a(n) = n+min(2*floor(a(n-1)/2), 3*floor(a(n-1)/3)) for n > 1, a(1)=1.
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0
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1, 2, 3, 6, 11, 15, 21, 28, 36, 46, 56, 66, 79, 92, 105, 120, 137, 153, 171, 190, 210, 232, 254, 276, 301, 326, 351, 378, 407, 435, 465, 496, 528, 562, 596, 630, 667, 704, 741, 780, 821, 861, 903, 946, 990, 1036, 1082, 1128, 1177, 1226, 1275, 1326, 1379, 1431
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| a(n) = n*(n-1)/2 + b(n) where b repeats the period (1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0) of length 12.
a(n) = +2*a(n-1) -a(n-2) +a(n-12) -2*a(n-13) +a(n-14).
G.f.: -x*(1+2*x^4-x^5+2*x^6+x^7+x^8+2*x^9+2*x^12+2*x^3) / ( (1+x) *(1+x^2) *(1+x+x^2) *(x^2-x+1) *(x^4-x^2+1) *(x-1)^3 ).
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CROSSREFS
| (MAGMA) [ n eq 1 select 1 else n+Min(2*Floor(Self(n-1)/2), 3*Floor(Self(n-1)/3)) : n in [1..60] ]; // Klaus Brockhaus, Dec 03 2010
(MAGMA) b:=func< n | [1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0][(n mod 12)+1] >; [ n*(n-1)/2+b(n-1): n in [1..60] ]; // Klaus Brockhaus, Dec 03 2010
Sequence in context: A163781 A090304 A005211 * A102990 A138520 A138519
Adjacent sequences: A076304 A076305 A076306 * A076308 A076309 A076310
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Nov 06 2002
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