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 A084468 #23 Apr 07 2025 10:05:46
%S A084468 7,11,13,19,21,25,35,37,41,49,67,69,73,81,97,131,133,137,145,161,193,
%T A084468 259,261,265,273,289,321,385,515,517,521,529,545,577,641,769,1027,
%U A084468 1029,1033,1041,1057,1089,1153,1281,1537,2051,2053,2057,2065,2081,2113,2177
%N A084468 Odd numbers with exactly 3 ones in binary expansion.
%H A084468 Amiram Eldar, <a href="/A084468/b084468.txt">Table of n, a(n) for n = 1..10000</a>
%H A084468 Robert Baillie, <a href="http://arxiv.org/abs/0806.4410">Summing the curious series of Kempner and Irwin</a>, arXiv:0806.4410 [math.CA], 2008-2015. See p. 18 for Mathematica code irwinSums.m.
%F A084468 a(n) = 2*A018900(n) + 1 = A005408(A018900(n)).
%F A084468 Sum_{n>=1} 1/a(n) = 0.714295772926319061998427422200268976390844375453066534198594764887682975019... (calculated using Baillie's irwinSums.m, see Links). - _Amiram Eldar_, Feb 14 2022
%t A084468 Flatten[Table[2^m + 2^n + 1, {m, 2, 11}, {n, m - 1}]] (* _Alonso del Arte_, Jul 08 2011 *)
%o A084468 (PARI) for(m=2, 9, for(n=1, m-1, print1(2^m+2^n+1", "))) \\ _Charles R Greathouse IV_, Oct 04 2011
%o A084468 (Python)
%o A084468 from math import isqrt, comb
%o A084468 def A084468(n): return (1<<(m:=isqrt(n<<3)+1>>1)+1)+(1<<(n-comb(m,2)))|1 # _Chai Wah Wu_, Apr 07 2025
%Y A084468 Intersection of A005408 and A014311.
%Y A084468 A084470(n) gives the position of a(n) in A084467(n).
%Y A084468 Cf. A018900.
%K A084468 nonn,base,easy
%O A084468 1,1
%A A084468 _Antti Karttunen_, Jun 02 2003