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A110344
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a(n)=Sum(n+k,k=0..n-1)=n(3n-1)/2 if n is even; a(n)=Sum(n-k,k=0..n-1)=n(n+1)/2 if n is odd.
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1
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1, 5, 6, 22, 15, 51, 28, 92, 45, 145, 66, 210, 91, 287, 120, 376, 153, 477, 190, 590, 231, 715, 276, 852, 325, 1001, 378, 1162, 435, 1335, 496, 1520, 561, 1717, 630, 1926, 703, 2147, 780, 2380, 861, 2625, 946, 2882, 1035, 3151, 1128, 3432, 1225, 3725, 1326
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(2n+1)=A000217(2n+1)=(n+1)(2n+1) (triangular numbers with odd index). a(2n)=A000326(2n)=A049452(n)=n(6n-1) (pentagonal numbers with even index) - Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 01 2005
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EXAMPLE
| a(3) = 3+2 +1 = 6.
a(6) = 6 +7 +8 +9 +10 +11 = 51.
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MAPLE
| a:=proc(n) if n mod 2=0 then n*(3*n-1)/2 else n*(n+1)/2 fi end: seq(a(n), n=1..60); (Deutsch)
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CROSSREFS
| Cf. A000217, A000326, A049452.
Sequence in context: A095308 A132796 A006492 * A135301 A192917 A030672
Adjacent sequences: A110341 A110342 A110343 * A110345 A110346 A110347
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KEYWORD
| easy,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 20 2005
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 01 2005
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