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A065221
Fill a triangular array by rows by writing numbers 1 up to b(0), 1 up to b(1), etc., where b(n) are the pentagonal numbers. The final elements of the rows form a(n).
17
1, 2, 5, 4, 9, 3, 10, 18, 5, 15, 26, 3, 16, 30, 45, 10, 27, 45, 64, 14, 35, 57, 80, 12, 37, 63, 90, 1, 30, 60, 91, 123, 11, 45, 80, 116, 153, 15, 54, 94, 135, 177, 10, 54, 99, 145, 192, 240, 42, 92, 143, 195, 248, 15, 70, 126, 183, 241, 300, 30, 91, 153, 216, 280, 345, 35
OFFSET
0,2
EXAMPLE
The array begins
....1
...1.2
..3.4.5
.1.2.3.4
5.6.7.8.9
CROSSREFS
Cf. A000326.
Mini-index to these sequences: A064766, A064865, A064866, A065221-A655234 are all of the same type. See A064766 for a detailed explanation.
Sequence in context: A198193 A316905 A214533 * A373053 A283419 A114752
KEYWORD
easy,nonn,changed
AUTHOR
Floor van Lamoen, Oct 22 2001
STATUS
approved