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Complement of the 11-gonal numbers.
1

%I #11 Oct 07 2024 01:18:36

%S 2,3,4,5,6,7,8,9,10,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,

%T 28,29,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,

%U 52,53,54,55,56,57,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,96,97,98,99,100,101,102

%N Complement of the 11-gonal numbers.

%F a(n) = n + floor(1/2+(2n/9+2/9)^(1/2)).

%t Table[n+Floor[1/2+(2n/9+2/9)^(1/2)], {n,100}]

%o (Python)

%o from math import isqrt

%o def A183223(n): return n+(isqrt((n<<3|4)//9)+1>>1) # _Chai Wah Wu_, Oct 06 2024

%Y Cf. A051682 (11-gonal numbers).

%K nonn

%O 1,1

%A _Clark Kimberling_, Jan 01 2011