A272081 Irregular triangle read by rows: strictly decreasing positive integer sequences in lexicographic order with the property that the sum of inverses is the inverse of an integer.

1, 2, 3, 4, 5, 6, 6, 3, 6, 3, 2, 7, 8, 9, 10, 11, 12, 12, 4, 12, 6, 12, 6, 4, 12, 6, 4, 2, 13, 14, 15, 15, 10, 15, 10, 3, 15, 10, 3, 2, 15, 10, 6, 15, 12, 10, 15, 12, 10, 4, 15, 12, 10, 4, 2, 15, 12, 10, 6, 4, 3, 16, 17, 18, 18, 9, 18, 9, 3, 18, 9, 3, 2, 18, 9

Offset

1,2

Links

Peter Kagey, Table of n, a(n) for n = 1..2170 (All rows with first term less than or equal to 30.)

Example

First 18 rows:
  [1]           because 1 is self-inverse.
  [2]           because 1/2 is the inverse of an integer.
  [3]
  [4]           (...)
  [5]
  [6]
  [6, 3]        because 1/6 + 1/3              = 1/2.
  [6, 3, 2]     because 1/6 + 1/3 + 1/2        = 1/1.
  [7]
  [8]
  [9]           (...)
  [10]
  [11]
  [12]
  [12, 4]       because 1/12 + 1/4             = 1/3.
  [12, 6]       because 1/12 + 1/6             = 1/4.
  [12, 6, 4]    because 1/12 + 1/6 + 1/4       = 1/2.
  [12, 6, 4, 2] because 1/12 + 1/6 + 1/4 + 1/2 = 1/1.

Crossrefs

Cf. A272020, A272034, A272082, A272083.

Sequence in context: A307089 A239132 A307311 * A317582 A293705 A036055

Adjacent sequences: A272078 A272079 A272080 * A272082 A272083 A272084

Keyword

nonn,tabf

Author

Peter Kagey, Apr 19 2016

Status

approved