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A317648
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a(1) = a(2) = 1; for n >= 3, a(n) = a(t(n)) + a(n-t(n)) where t = A004001.
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5
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1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 7, 7, 7, 8, 8, 9, 9, 10, 11, 12, 12, 12, 12, 13, 14, 15, 15, 15, 15, 16, 16, 17, 17, 18, 19, 20, 21, 21, 21, 21, 21, 22, 23, 24, 25, 26, 27, 27, 27, 27, 27, 27, 27, 28, 29, 30, 31, 31, 31, 31, 31, 32, 32, 33, 33, 34, 35, 36, 37, 38, 38, 38, 38, 38, 38, 39, 40, 41, 42, 43, 44, 45
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OFFSET
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1,3
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COMMENTS
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This sequence hits every positive integer.
Let b(1) = b(2) = b(3) = 1; for n >= 4, b(n) = b(t(n)) + b(n-t(n)) where t = A004001. Observe the symmetric relation between this sequence (a(n)) and b(n) thanks to line plots of a(n)-n/2 and b(n)-n/2 in Links section.
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LINKS
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FORMULA
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a(n+1) - a(n) = 0 or 1 for all n >= 1.
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MAPLE
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b:= proc(n) option remember; `if`(n<3, 1,
b(b(n-1)) +b(n-b(n-1)))
end:
a:= proc(n) option remember; `if`(n<3, 1,
a(b(n)) +a(n-b(n)))
end:
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MATHEMATICA
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t[1] = 1; t[2] = 1; t[n_] := t[n] = t[t[n-1]] + t[n - t[n-1]];
a[1] = a[2] = 1; a[n_] := a[n] = a[t[n]] + a[n - t[n]];
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PROG
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(PARI) t=vector(99); t[1]=t[2]=1; for(n=3, #t, t[n] = t[t[n-1]]+t[n-t[n-1]]); a=vector(99); a[1]=a[2]=1; for(n=3, #a, a[n] = a[t[n]]+a[n-t[n]]); a
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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