A339389 a(n) is the number of ordered pairs (i, j) of numbers in the range 1..n-1 such that a(i) + a(j) >= a(n-1).

0, 1, 3, 5, 8, 12, 14, 21, 21, 38, 23, 68, 24, 114, 28, 149, 36, 182, 47, 209, 60, 247, 68, 315, 70, 397, 68, 515, 71, 605, 82, 667, 106, 690, 147, 700, 206, 717, 255, 747, 282, 835, 244, 1103, 160, 1462, 124, 1751, 131, 1913, 160, 1990, 213, 1988, 324, 1771

Offset

1,3

Comments

Graphically, we have two curves that correspond to the bisections (see illustration in Links section).

Links

Rémy Sigrist, Table of n, a(n) for n = 1..10000

Rémy Sigrist, Colored scatterplot of the first 25000 terms (where the color denotes the parity of n)

Rémy Sigrist, C program for A339389

Prog

(PARI) { for (n=1, #a = vector(56), print1 (a[n] = sum(i=1, n-1, sum(j=1, n-1, a[i]+a[j]>=a[n-1])) ", ")) }
(C) See Links section.

Crossrefs

Cf. A339388.

Sequence in context: A114891 A285953 A287380 * A348236 A218485 A310029

Adjacent sequences: A339386 A339387 A339388 * A339390 A339391 A339392

Keyword

nonn,look

Author

Rémy Sigrist, Dec 02 2020

Status

approved