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Search: id:A125777
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| 1, 3, 6, 13, 28, 21, 69, 161, 137, 55, 433, 1078, 1017, 477, 120, 3141, 8245, 8437, 4460, 1337, 231, 25873, 71008, 77620, 45058, 15415, 3220, 406, 238629, 680451, 786012, 492264, 186729, 44955, 6930, 666, 2436673, 7184170, 8699205, 5804448, 2394150
(list; table; graph; listen)
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OFFSET
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1,2
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COMMENT
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Left border = A104989: (1, 3, 13, 69, 433...). Right border = the doubly triangular numbers starting (1, 6, 21...): A002817.
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REFERENCES
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J. H. Conway and R. K. Guy, "The Book of Numbers", Springer-Verlag, 1996, p. 64.
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LINKS
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Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Jun 17 2007, Table of n, a(n) for n = 1..55
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FORMULA
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Begin with the triangular numbers A000217 and circle every T(k)-th term, getting the doubly triangular numbers, A002817. Per instructions shown in A125714, take partial sums of the uncircled terms in row 1, denoting this as row 2. Circle the row 2 terms which are one place to the left of row 1 terms. Take partial sums again in analogous operations for subsequent rows.
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EXAMPLE
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First few rows of the triangle are:
1;
3, 6;
13, 28, 21;
69, 161, 137, 55;
433, 1078, 1017, 477, 120;
...
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CROSSREFS
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Cf. A125714, A002817, A104989, A000217.
Sequence in context: A036886 A052251 A032253 this_sequence A103788 A106461 A095768
Adjacent sequences: A125774 A125775 A125776 this_sequence A125778 A125779 A125780
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KEYWORD
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nonn,tabl
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AUTHOR
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Gary W. Adamson (qntmpkt(AT)yahoo.com), Dec 07 2006
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EXTENSIONS
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More terms from Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Jun 17 2007
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