A340520 a(n) = 2*A006463(n) + 1.

1, 3, 5, 9, 13, 17, 23, 29, 35, 41, 49, 57, 65, 73, 81, 91, 101, 111, 121, 131, 141, 153, 165, 177, 189, 201, 213, 225, 239, 253, 267, 281, 295, 309, 323, 337, 353, 369, 385, 401, 417, 433, 449, 465, 481, 499, 517, 535, 553, 571, 589, 607, 625, 643, 661, 681, 701, 721, 741, 761, 781, 801

Offset: 1

Author

N. J. A. Sloane, Feb 04 2021

Keywords

• nonn

Comments

Index of start of row n in b-files for triangles (such as A237593, A262045) where the rows have length 2*A003056(n).

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003056, A006463, A237593, A262045.

Programs

Python

from math import isqrt
def A340520(n): return (m:=isqrt((n<<3)+1)-1>>1)*(6*n-2-m*(m+3))//3|1 # Chai Wah Wu, Jun 07 2025