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A161904
Array read by rows in which row n list the divisors of n, but if n is a square then the square root of n appears repeated. Also, the divisors appear as pairs (a,b), where a <= b, such that a*b = n.
5
1, 1, 1, 2, 1, 3, 1, 4, 2, 2, 1, 5, 1, 6, 2, 3, 1, 7, 1, 8, 2, 4, 1, 9, 3, 3, 1, 10, 2, 5, 1, 11, 1, 12, 2, 6, 3, 4, 1, 13, 1, 14, 2, 7, 1, 15, 3, 5, 1, 16, 2, 8, 4, 4, 1, 17, 1, 18, 2, 9, 3, 6, 1, 19, 1, 20, 2, 10, 4, 5, 1, 21, 3, 7
OFFSET
1,4
COMMENTS
Row lengths are 2*A038548(n). - R. J. Mathar Jun 28 2009
EXAMPLE
Array begins:
(1,1);
(1,2);
(1,3);
(1,4),(2,2);
(1,5);
(1,6),(2,3);
(1,7);
(1,8),(2,4);
(1,9),(3,3);
(1,10),(2,5);
(1,11);
(1,12),(2,6),(3,4);
(1,13);
(1,14),(2,7);
(1,15),(3,5);
(1,16),(2,8),(4,4);
CROSSREFS
See also A161901 for another version.
Sequence in context: A375266 A067734 A303758 * A360678 A346697 A338565
KEYWORD
easy,nonn,tabf
AUTHOR
Omar E. Pol, Jun 23 2009
EXTENSIONS
Keyword tabf added by R. J. Mathar, Jun 28 2009
STATUS
approved