%I #11 Oct 05 2024 10:13:12
%S 2,3,4,5,6,8,9,10,11,12,13,14,15,16,17,19,20,21,22,23,24,25,26,27,28,
%T 29,30,31,32,33,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,
%U 53,54,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106
%N Complement of the heptagonal (7-gonal) numbers.
%F n+Floor[1/2+(2n/5)^(1/2)].
%e 7-gonal numbers: (1,7,18,34,55,...)=A000566, so that
%e A183219=(2,3,4,5,6,8,9,...17,19,...33,35,...).
%t Table[n+Floor[1/2+(2n/5)^(1/2)], {n,100}]
%t Module[{nn=7,heps},heps=PolygonalNumber[7,Range[nn]];Complement[Range[Last[heps]],heps]] (* _Harvey P. Dale_, Apr 02 2023 *)
%o (Python)
%o from math import isqrt
%o def A183219(n): return n+(isqrt((n<<3)//5)+1>>1) # _Chai Wah Wu_, Oct 05 2024
%Y Cf. A000566.
%K nonn
%O 1,1
%A _Clark Kimberling_, Jan 01 2011