|
Search: id:A074486
|
|
|
| A074486 |
|
Decimal encoding of topologies generated by classes of sets: map {}, a, b, c, d, ... to 1, 2, 4, 16, 256, ...i.e. ( 2^0, 2^1, 2^2, 2^4, 2^8, ...). |
|
+0
2
|
|
| 1, 3, 9, 11, 15, 129, 131, 137, 139, 143, 153, 171, 175, 255
(list; graph; listen)
|
|
|
OFFSET
|
0,2
|
|
|
COMMENT
|
The sequence encodes unlabeled topologies as described in A000798. For example, a(3)= 1+2+8 = 11 since {}, a,ab is the least decimal encoding. 1+4+8 = 13 since {}, b,ab.But is topologically equivalent; so is not in a(n). The number of equivalent cases corresponding to a(n) begins 1; 1,1,2; 1,1,3,3,6,3,3,3,6; ... and is counted by A001928 (labeled topologies).
|
|
EXAMPLE
|
a(11) = 171 because we can map {}, a, ab, ac, abc to 1 + 2 + 8 + 32 + 128
|
|
CROSSREFS
|
Cf. A000798.
Sequence in context: A106373 A059326 A028312 this_sequence A131861 A131859 A096187
Adjacent sequences: A074483 A074484 A074485 this_sequence A074487 A074488 A074489
|
|
KEYWORD
|
more,nonn
|
|
AUTHOR
|
Alford Arnold (Alford1940(AT)aol.com), Sep 26 2002
|
|
|
Search completed in 0.002 seconds
|
