A341218 a(n) is the number of numbers k such that A340873(k) = n.

1, 1, 1, 2, 3, 4, 6, 8, 11, 15, 21, 29, 40, 54, 74, 102, 139, 189, 259, 355, 486, 664, 908, 1242, 1697, 2317, 3165, 4326, 5911, 8076, 11034, 15073, 20588, 28125, 38415, 52477, 71692, 97931, 133774, 182739, 249634, 341013, 465839, 636346, 869279, 1187486

Offset: 0

Author

Rémy Sigrist, Feb 07 2021

Keywords

• nonn
• base

Examples

			The first terms, alongside the correspond k's, are:
   n  a(n)  k's
   -  ----  ----------------------
   0     1              1
                        |
   1     1              2
                        |
   2     1              4
                       / \
   3     2            3   8
                     /   / \
   4     3          6   7   16
                   /   /   /  \
   5     4       12  14  15    32
		

Links

• Rémy Sigrist, PARI program for A341218
• Index entries for sequences related to 3x+1 (or Collatz) problem

Crossrefs

Cf. A005186, A340873.

Programs

PARI

See Links section.

Formula

a(n) <= a(n+1) <= 2*a(n).