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 A183217 #22 Oct 05 2024 10:26:09
%S A183217 2,3,4,6,7,8,9,10,11,13,14,15,16,17,18,19,20,21,23,24,25,26,27,28,29,
%T A183217 30,31,32,33,34,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,52,53,54,
%U A183217 55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,93
%N A183217 Complement of the pentagonal numbers.
%H A183217 Kevin Ryde, <a href="/A183217/b183217.txt">Table of n, a(n) for n = 1..10000</a>
%F A183217 a(n) = n + floor(1/2+(2n/3)^(1/2)).
%F A183217 a(n) = n + A111651(n). - _Kevin Ryde_, Aug 31 2024
%e A183217 The pentagonal numbers A000326 = (1,5,12,22,35,...), so that this sequence = (2,3,4,6,7,8,9,10,11,13,14,...).
%t A183217 Table[n+Floor[1/2+(2n/3)^(1/2)], {n,100}]
%o A183217 (PARI) a(n) = n + sqrtint(24*n)\/6; \\ _Kevin Ryde_, Aug 31 2024
%o A183217 (Python)
%o A183217 from math import isqrt
%o A183217 def A183217(n): return n+(isqrt((n<<3)//3)+1>>1) # _Chai Wah Wu_, Oct 05 2024
%Y A183217 Cf. A000326, A111651.
%K A183217 nonn,easy
%O A183217 1,1
%A A183217 _Clark Kimberling_, Jan 01 2011