A387644 Complement of A045944.

1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72

Offset

1,2

Links

James C. McMahon, Table of n, a(n) for n = 1..10000

Chai Wah Wu, Algorithms for Complementary Sequences, Integers (2025) Vol. 25, Art. No. A95. See p. 24.

Formula

a(n) = n+m if n > m*(3*m+1) and a(n) = n+m-1 otherwise where m = floor(sqrt(n/3)).

Mathematica

lim=72; limt=Ceiling[Sqrt[lim/3]]; Complement[Range[lim], Table[n*(3n+2), {n, 0, limt}] ] (* James C. McMahon, Sep 07 2025 *)

Prog

(Python)
from math import isqrt
def A387644(n): return n+(m:=isqrt(n//3))-(n<=m*(3*m+1))

Crossrefs

Cf. A045944.

Sequence in context: A231237 A053241 A340288 * A132329 A388077 A230313

Adjacent sequences: A387641 A387642 A387643 * A387645 A387646 A387647

Keyword

nonn,easy

Author

Chai Wah Wu, Sep 04 2025

Status

approved