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 A049890 #23 May 06 2022 13:12:15
%S A049890 1,1,2,3,6,12,24,47,93,188,376,751,1501,2999,5992,11972,23921,47888,
%T A049890 95776,191551,383101,766199,1532392,3064772,6129521,12258996,24517897,
%U A049890 49035606,98070837,196140924,392280350,784557707,1569109434
%N A049890 a(n) = a(1) + a(2) + ... + a(n-1) - a(m) for n >= 4, where m = n - 1 - 2^p and p is the unique integer such that 2^p < n - 1 <= 2^(p+1), starting with a(1) = a(2) = 1 and a(3) = 2.
%o A049890 (PARI) lista(nn) = { nn = max(nn, 3); my(va = vector(nn)); va[1] = 1; va[2] = 1; va[3] = 2; my(sa = vecsum(va)); for (n=4, nn, va[n] = sa - va[n - 1 - 2^logint(n-2,2)]; sa += va[n]; ); va; } \\ _Petros Hadjicostas_, Apr 27 2020
%Y A049890 Cf. A049891 (similar, but with minus a(2*m)), A049938 (similar, but with plus a(m)), A049939 (similar, but with plus a(2*m)).
%K A049890 nonn
%O A049890 1,3
%A A049890 _Clark Kimberling_
%E A049890 Name edited by _Petros Hadjicostas_, Apr 27 2020