A056133 - OEIS

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A056133

a(1) = 1, a(m+1) = sum_{k=1 to m}[min(m, a(k))].

1, 1, 2, 4, 8, 13, 20, 29, 40, 52, 66, 82, 100, 120, 141, 164, 189, 216, 245, 276, 309, 343, 379, 417, 457, 499, 543, 589, 637, 687, 738, 791, 846, 903, 962, 1023, 1086, 1151, 1218, 1287, 1358, 1430, 1504, 1580, 1658, 1738, 1820, 1904, 1990, 2078, 2168

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OFFSET

1,3

COMMENTS

This sequence can also be defined as follows: a(n) is the unique sequence such that a(1) = a(2) = 1 and the second differences of a(n) are 2, except that the a(n)th second difference is 1 for all n. In other words, if b(n) = a(n+2) - 2a(n+1) + a(n) is the second-difference function for a(n), x(n) = 2 - b(n) is the characteristic function for a(n). - Joel B. Lewis, Mar 16 2007

LINKS

Table of n, a(n) for n=1..51.

EXAMPLE

a(6) = min(5,1) + min(5,1) + min(5,2) + min(5,4) + min(5,8) = 1 + 1 + 2 + 4 + 5 = 13.

CROSSREFS

Sequence in context: A164486 A084684 A011907 * A172131 A173721 A164482

Adjacent sequences: A056130 A056131 A056132 * A056134 A056135 A056136

KEYWORD

easy,nonn

AUTHOR

Leroy Quet, Aug 04 2000

STATUS

approved