A183221 Complement of the 9-gonal numbers.

2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105

Offset

1,1

Links

Table of n, a(n) for n=1..100.

Formula

a(n) = n + floor(1/2+(2n/7)^(1/2)).

Mathematica

Table[n+Floor[1/2+(2n/7)^(1/2)], {n, 100}]

Prog

(Python)
from math import isqrt
def A183221(n): return n+(isqrt((n<<3)//7)+1>>1) # Chai Wah Wu, Oct 05 2024

Crossrefs

Cf. A001106 (9-gonal numbers).

Sequence in context: A376573 A072886 A031980 * A317492 A324721 A327534

Adjacent sequences: A183218 A183219 A183220 * A183222 A183223 A183224

Keyword

nonn

Author

Clark Kimberling, Jan 01 2011

Status

approved