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A064865 Fill a triangular array by rows by writing numbers 1, then 1 up to 2^2, then 1 up to 3^2, then 1 up to 4^2 and so on. The final elements of the rows form the sequence. 17
1, 2, 1, 5, 1, 7, 14, 6, 15, 25, 11, 23, 36, 14, 29, 45, 13, 31, 50, 6, 27, 49, 72, 15, 40, 66, 93, 21, 50, 80, 111, 22, 55, 89, 124, 16, 53, 91, 130, 1, 42, 84, 127, 171, 20, 66, 113, 161, 210, 35, 86, 138, 191, 245, 44, 100, 157, 215, 274, 45, 106, 168, 231, 295, 36 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Does every number appear at least once? Do some numbers like 1 appear infinitely often? - Robert G. Wilson v, Oct 10 2001

Difference between n-th triangular number and largest square pyramidal number (A000330) less than it. - Franklin T. Adams-Watters, Sep 11 2006

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = n(n+1)/2 - max_{p(m) < n(n+1)/2} p(m), where p(m) = m(m+1)(2m+1)/6. - Franklin T. Adams-Watters, Sep 11 2006

EXAMPLE

The triangle begins:

....1

...1.2

..3.4.1

.2.3.4.5

6.7.8.9.1

MATHEMATICA

a = {}; Do[a = Append[a, Table[i, {i, 1, n^2} ]], {n, 1, 100} ]; a = Flatten[a]; Do[Print[a[[n(n + 1)/2]]], {n, 1, 100} ]

CROSSREFS

Table: A064866.

Cf. A000217, A000330.

Sequence in context: A263454 A036073 A124227 * A178472 A331888 A178470

Adjacent sequences:  A064862 A064863 A064864 * A064866 A064867 A064868

KEYWORD

easy,nonn

AUTHOR

Floor van Lamoen, Oct 08 2001

EXTENSIONS

More terms from Robert G. Wilson v, Oct 10 2001

STATUS

approved

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Last modified April 3 04:21 EDT 2020. Contains 333195 sequences. (Running on oeis4.)