A343081 a(n) is the smallest number that is the sum of n positive cubes in three or more ways.

5104, 1225, 766, 221, 222, 223, 224, 197, 163, 164, 165, 166, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177

Offset

3,1

Comments

This is r(n,3,3) in Alter's notation.

Links

Table of n, a(n) for n=3..53.

R. Alter, Computations and generalizations on a remark of Ramanujan, pp. 182-196 of "Analytic Number Theory (Philadelphia, 1980)", ed. M. I. Knopp, Lect. Notes Math., Vol. 899, 1981. See Table 7, page 192.

Index entries for linear recurrences with constant coefficients, signature (2,-1).

Formula

a(n) = n + 124 for n >= 15.

Example

a(3) = 5104 = 1^3 + 12^3 + 15^3 = 2^3 + 10^3 + 16^3 = 9^3 + 10^3 + 15^3.
a(4) = 1225 = 1^3 + 2^3 + 6^3 + 10^3 = 3^3 + 7^3 + 7^3 + 8^3 = 4^3 + 6^3 + 6^3 + 9^3.
a(9) = 224 = 6^3 + 8*1^3 = 3*4^3 + 3^3 + 5*1^3 = 5^3 + 4^3 + 4*2^3 + 3*1^3.

Crossrefs

Cf. A342902, A343080, A343082, A343083, A343085.

Sequence in context: A135842 A224492 A330730 * A219329 A025398 A025397

Adjacent sequences: A343078 A343079 A343080 * A343082 A343083 A343084

Keyword

nonn,easy

Author

Sean A. Irvine, Apr 04 2021

Extensions

Corrected by Robert Israel, Apr 05 2021

a(9) reverted by Sean A. Irvine, Apr 18 2021

Status

approved