A357379 a(n) = A357378(floor(n/2)) * A357378(n).

1, 2, 4, 6, 8, 10, 3, 9, 12, 16, 5, 15, 7, 11, 18, 21, 24, 27, 20, 28, 13, 14, 30, 33, 35, 42, 22, 44, 36, 48, 49, 56, 32, 40, 45, 54, 25, 50, 63, 70, 26, 39, 84, 98, 60, 80, 55, 66, 65, 75, 72, 78, 34, 38, 52, 64, 90, 96, 88, 104, 77, 91, 112, 120, 68, 76, 85

Offset

0,2

Comments

This sequence is a bijection from the nonnegative integers to the positive integers with inverse A357396 (see comments in A357378).

Links

Rémy Sigrist, Table of n, a(n) for n = 0..10000

Rémy Sigrist, Density plot of the first 10000000 terms

Rémy Sigrist, C program

Index entries for sequences that are permutations of the natural numbers

Example

a(5) = A357378(floor(5/2)) * A357378(5) = A357378(2) * A357378(5) = 2 * 5 = 10.

Prog

(C) See Links section.
(Python)
from itertools import count, islice
def agen(): # generator of terms
    alst, disallowed = [1], {1}; yield 1
    for n in count(1):
        ahalf, k = alst[n//2], 1
        while ahalf*k in disallowed: k += 1
        an = k; yield ahalf*an; alst.append(an); disallowed.add(ahalf*an)
print(list(islice(agen(), 67))) # Michael S. Branicky, Sep 26 2022

Crossrefs

Cf. A357378, A357396 (inverse).

Sequence in context: A004522 A004521 A103694 * A083167 A338741 A115950

Adjacent sequences: A357376 A357377 A357378 * A357380 A357381 A357382

Keyword

nonn

Author

Rémy Sigrist, Sep 26 2022

Status

approved