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A215655
Irregular triangle read by rows: reading the n-th row describes all the numbers seen in the triangle up to the end of the n-th row.
0
2, 2, 4, 2, 2, 4, 6, 2, 4, 4, 2, 6, 8, 2, 6, 4, 4, 6, 2, 8, 10, 2, 8, 4, 6, 6, 4, 8, 2, 10, 12, 2, 10, 4, 8, 6, 6, 8, 4, 10, 2, 12, 14, 2, 12, 4, 10, 6, 8, 8, 6, 10, 4, 12, 2, 14, 16, 2, 14, 4, 12, 6, 10, 8, 8, 10, 6, 12, 4, 14, 2, 16, 18, 2, 16, 4, 14, 6, 12, 8, 10, 10, 8, 12, 6, 14, 4, 16, 2, 18, 20, 2, 18, 4, 16, 6, 14, 8, 12, 10, 10, 12, 8, 14, 6, 16, 4, 18, 2, 20
OFFSET
1,1
COMMENTS
Given the initial row "2 2", is the rest of the triangle forced? If not, should this version have an additional clause in the definition saying "lexicographically earliest, given the first row"?
Eric Angelini asks if there is a similar triangle (self-describing and infinite) that contains at least one odd number.
REFERENCES
Eric Angelini, Posting to the Sequence Fans Mailing List, Oct 29 2012.
EXAMPLE
Triangle begins:
2 2
4 2 2 4
6 2 4 4 2 6
8 2 6 4 4 6 2 8
10 2 8 4 6 6 4 8 2 10
12 2 10 4 8 6 6 8 4 10 2 12
14 2 12 4 10 6 8 8 6 10 4 12 2 14
16 2 14 4 12 6 10 8 8 10 6 12 4 14 2 16
18 2 16 4 14 6 12 8 10 10 8 12 6 14 4 16 2 18
20 2 18 4 16 6 14 8 12 10 10 12 8 14 6 16 4 18 2 20
...
Top line says: I see two integers "2" so far
Next line says: I see four integers "2" and two integers "4" so far
Next line says: I see six integers "2", four integers "4" and two integers "6" so far
etc.
The counts are thus cumulative. And the (easy-to-build) array infinite.
CROSSREFS
Cf. A005150.
Sequence in context: A276604 A072301 A127171 * A118232 A115070 A064145
KEYWORD
nonn,tabf
AUTHOR
N. J. A. Sloane, Feb 17 2013
STATUS
approved