OFFSET
1,3
COMMENTS
Parity of n and a(n) is opposite.
It is unknown whether all positive integers arise in A080383 or not.
a(22)=16357, a(23)=90306, a(26)=90307. - Vaclav Kotesovec, Sep 10 2019
For each n > 20 except 22, 23, and 26, a(n) > 10^6 (if it exists). - Jon E. Schoenfield, Sep 15 2019
EXAMPLE
a(10)=13 because in A080383 10 appears first as the 13th term.
MATHEMATICA
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
PROG
(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
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Mar 17 2003
EXTENSIONS
a(13)-a(16) from Michel Marcus, Aug 23 2019
a(17) from Jon E. Schoenfield, Sep 15 2019
a(18) from Michel Marcus, Aug 23 2019
a(19) from Vaclav Kotesovec, Sep 10 2019
a(20) from Jon E. Schoenfield, Sep 15 2019
STATUS
approved