|
Search: id:A128400
|
|
|
| A128400 |
|
Numbers n such that n^2 divides 20^n-1. |
|
+0
15
|
| |
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
19 divides a(n) for n>1. a(n) is a subset of A128360(n) = {1, 19, 361, 6859, 130321, 2476099, 47045881, 148305659, ...} Numbers n such that n divides 20^n-1.
|
|
MATHEMATICA
|
a={}; Do[r=(20^n-1)/n^2; If[r==IntegerPart[r], AppendTo[a, n]], {n, 1, 10^3}]; a [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Aug 07 2008]
|
|
CROSSREFS
|
Cf. A128360 = numbers n such that n divides 20^n-1. Cf. A127103, A127104, A127105, A127106, A127107, A127102, A127101, A127100, A127092, A128405, A128393, A128394, A128395, A128396, A128397, A128398, A128399, A128400, A128401, A128402, A128403, A128404.
Sequence in context: A087515 A038028 A013890 this_sequence A133591 A137643 A023921
Adjacent sequences: A128397 A128398 A128399 this_sequence A128401 A128402 A128403
|
|
KEYWORD
|
bref,hard,more,nonn
|
|
AUTHOR
|
Alexander Adamchuk (alex(AT)kolmogorov.com), Mar 08 2007
|
|
|
Search completed in 0.002 seconds
|
