This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A080393 #39 Sep 19 2019 01:45:21
%S A080393 0,1,2,3,40,5,12,25,1122,13,420,1103,12324,421,4960,11289,232582,4961,
%T A080393 16356,107073
%N A080393 a(n) is the smallest integer such that A080383(a(n)) = n.
%C A080393 Parity of n and a(n) is opposite.
%C A080393 It is unknown whether all positive integers arise in A080383 or not.
%C A080393 a(22)=16357, a(23)=90306, a(26)=90307. - _Vaclav Kotesovec_, Sep 10 2019
%C A080393 For each n > 20 except 22, 23, and 26, a(n) > 10^6 (if it exists). - _Jon E. Schoenfield_, Sep 15 2019
%e A080393 a(10)=13 because in A080383 10 appears first as the 13th term.
%t A080393 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
%o A080393 (PARI) f(n) = my(b=binomial(n, n\2)); sum(i=0, n, (b % binomial(n, i)) == 0); \\ A080383
%o A080393 a(n) = my(k=0); while(f(k) != n, k++); k; \\ _Michel Marcus_, Aug 23 2019
%Y A080393 Cf. A080383, A080384(1)=a(6), A080385(1)=a(7), A080386(1)=a(8), A080387(1)=a(10).
%K A080393 nonn,more
%O A080393 1,3
%A A080393 _Labos Elemer_, Mar 17 2003
%E A080393 a(13)-a(16) from _Michel Marcus_, Aug 23 2019
%E A080393 a(17) from _Jon E. Schoenfield_, Sep 15 2019
%E A080393 a(18) from _Michel Marcus_, Aug 23 2019
%E A080393 a(19) from _Vaclav Kotesovec_, Sep 10 2019
%E A080393 a(20) from _Jon E. Schoenfield_, Sep 15 2019