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A080393
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a(n) is the smallest integer such that A080383(a(n)) = n.
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1
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0, 1, 2, 3, 40, 5, 12, 25, 1122, 13, 420, 1103, 12324, 421, 4960, 11289, 232582, 4961, 16356, 107073
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OFFSET
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1,3
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COMMENTS
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Parity of n and a(n) is opposite.
It is unknown whether all positive integers arise in A080383 or not.
For each n > 20 except 22, 23, and 26, a(n) > 10^6 (if it exists). - Jon E. Schoenfield, Sep 15 2019
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LINKS
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EXAMPLE
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a(10)=13 because in A080383 10 appears first as the 13th term.
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MATHEMATICA
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f[x_] := Count[Table[IntegerQ[Binomial[x, Floor[x/2]]/ Binomial[x, j]], {j, 0, n}], True]; t=Table[0, {20}]; Do[s=f[n]; If[s<21&&t[[s]]==0, t[[s]]=n], {n, 1, 1300}]; t
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PROG
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(PARI) f(n) = my(b=binomial(n, n\2)); sum(i=0, n, (b % binomial(n, i)) == 0); \\ A080383
a(n) = my(k=0); while(f(k) != n, k++); k; \\ Michel Marcus, Aug 23 2019
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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