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 A229949 #19 Dec 03 2023 05:01:59 %S A229949 1,2,3,4,3,6,5,6,3,8,9,8,3,8,7,12,5,12,9,8,3,12,15,12,3,8,9,16,9,20,9, %T A229949 10,3,12,15,12,3,12,15,24,9,16,9,8,3,16,21,24,5,12,9,16,7,24,15,12,3, %U A229949 16,27,16,3,12,11,24,9,16,9,16,9,36,25,18,3,8 %N A229949 Number of divisors of the n-th positive quarter-square. %C A229949 Also A048691 and A092517 interleaved. %C A229949 The first bisection gives A048691, the number of divisors of the squares. The second bisection gives A092517, the number of divisors of the oblong numbers. %C A229949 a(n) has the same parity of n. %H A229949 Amiram Eldar, <a href="/A229949/b229949.txt">Table of n, a(n) for n = 1..10000</a> %F A229949 a(n) = A000005(A002620(n+1)). %t A229949 a[n_] := DivisorSigma[0, Floor[(n+1)^2/4]]; Array[a, 100] (* _Amiram Eldar_, Dec 03 2023 *) %o A229949 (PARI) a(n) = numdiv((n+1)^2\4); \\ _Amiram Eldar_, Dec 03 2023 %Y A229949 Cf. A000005, A000290, A002378, A002620, A048691, A092517, A220492. %K A229949 nonn,easy %O A229949 1,2 %A A229949 _Omar E. Pol_, Oct 24 2013