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A174232
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a(n) = a(n-1) - (-1)^n*n if (A004001(n) mod 3) = 1, otherwise a(n-1) + (-1)^n*n.
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2
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1, 0, -2, -5, -1, -6, -12, -5, -13, -22, -12, -1, -13, -26, -12, -27, -11, -28, -46, -65, -45, -66, -88, -111, -87, -112, -86, -113, -141, -112, -142, -111, -143, -176, -142, -107, -71, -108, -70, -31, 9, -32, 10, 53, 97, 52, 98, 51, 99, 148, 198, 147, 199, 146
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) = a(n-1) - (-1)^n*n if (A004001(n) mod 3) = 1, otherwise a(n-1) + (-1)^n*n, with a(0) = 1 and a(1) = 0.
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MATHEMATICA
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HC[n_]:= HC[n]= If[n<3, Fibonacci[n], HC[HC[n-1]] +HC[n -HC[n-1]]]; (*A004001*)
a[n_]:= a[n]= If[n<2, 1-n, If[Mod[HC[n], 3]==1, a[n-1] -(-1)^n*n, a[n-1] + (-1)^n*n]];
Table[a[n], {n, 0, 80}]
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PROG
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(Sage)
@CachedFunction
if (n<3): return fibonacci(n)
else: return HC(HC(n-1)) +HC(n -HC(n-1))
if (n<2): return 1-n
elif (HC(n)%3==1): return A174232(n-1) - (-1)^n*n
else: return A174232(n-1) + (-1)^n*n
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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