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A289761 Maximum length of a perfect Wichmann ruler with n segments. 3
3, 6, 9, 12, 15, 22, 29, 36, 43, 50, 57, 68, 79, 90, 101, 112, 123, 138, 153, 168, 183, 198, 213, 232, 251, 270, 289, 308, 327, 350, 373, 396, 419, 442, 465, 492, 519, 546, 573, 600, 627, 658, 689, 720, 751, 782, 813, 848, 883, 918, 953, 988, 1023, 1062, 1101, 1140, 1179, 1218, 1257, 1300, 1343, 1386, 1429 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

For definitions see A103294.

LINKS

Hugo Pfoertner, Table of n, a(n) for n = 2..10001

Peter Luschny, Are optimal rulers of Wichmann type?

B. Wichmann, A note on restricted difference bases, J. Lond. Math. Soc. 38 (1963), 465-466.

FORMULA

a(n) = ( n^2 - (mod(n,6)-3)^2 ) / 3 + n.

Conjectures from Colin Barker, Jul 14 2017: (Start)

G.f.: x^2*(3 + 4*x^5 - 3*x^6) / ((1 - x)^3*(1 + x)*(1 - x + x^2)*(1 + x + x^2)).

a(n) = 2*a(n-1) - a(n-2) + a(n-6) - 2*a(n-7) + a(n-8) for n>9.

(End)

MATHEMATICA

Table[(n^2 - (Mod[n, 6] - 3)^2)/3 + n, {n, 2, 66}] (* Michael De Vlieger, Jul 14 2017 *)

PROG

(PARI) a(n) = n + (n^2 - (n%6 - 3)^2)/3; \\ Michel Marcus, Jul 14 2017

CROSSREFS

Cf. A004137, A103294, A193802, A193803, A289873.

Sequence in context: A123581 A187337 A184999 * A310151 A310152 A189783

Adjacent sequences:  A289758 A289759 A289760 * A289762 A289763 A289764

KEYWORD

nonn,easy

AUTHOR

Hugo Pfoertner, Jul 12 2017

STATUS

approved

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Last modified September 16 06:21 EDT 2019. Contains 327090 sequences. (Running on oeis4.)