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 A276188 #17 Jun 29 2024 16:42:54
%S A276188 3,99,577,3363
%N A276188 Numbers k > 1 such that the number of odd divisors of k-1 is odd and is equal to the number of odd divisors of k+1.
%C A276188 Conjecture: this sequence is finite.
%C A276188 Any further terms are greater than 10^10. - _Charles R Greathouse IV_, Aug 22 2016
%e A276188 99 is in this sequence because there are 3 odd divisors 1, 7 and 49 of 98 and there are 3 odd divisors 1, 5 and 25 of 100, and 3 is odd.
%t A276188 odo[n_]:=Module[{c=Select[Divisors[n],OddQ]},If[OddQ[Length[c]],Length[c],0]]; Flatten[ Position[ Partition[Array[odo,3500],3,1],_?(AllTrue[{#[[1]],#[[3]]},OddQ]&&#[[1]]==#[[3]]&),1,Heads->False]]+1 (* _Harvey P. Dale_, Apr 07 2023 *)
%o A276188 (Magma) [n: n in [2..100000] | NumberOfDivisors(2*(n-1))- NumberOfDivisors(n-1) eq NumberOfDivisors(2*(n+1))-NumberOfDivisors(n+1) and ((NumberOfDivisors(2*(n+1))- NumberOfDivisors(n+1)) mod 2) eq 1 ];
%Y A276188 Cf. A275418, A275598, A276136.
%K A276188 nonn,more
%O A276188 1,1
%A A276188 _Juri-Stepan Gerasimov_, Aug 23 2016