OFFSET
0,1
EXAMPLE
a(0) = 4 because the smallest number that cannot be represented as a sum of 3 nonnegative cubes is 4.
a(1) = 0 is the sum of three 0's.
a(2) = 216 = 3^3 + 4^3 + 5^3 = 6^3 + 0 + 0.
a(3) = 5104 = 1 + 12^3 + 15^3 = 2^3 + 10^3 + 16^3 = 9^3 + 10^3 + 15^3.
PROG
(Python)
TOP = 6000000
a = [0]*TOP
for b in range(TOP):
b3 = b**3
if b3*3>=TOP: break
for c in range(b, TOP):
c3 = b3 + c**3
if c3>=TOP: break
for d in range(c, TOP):
res = c3 + d**3
if res>=TOP: break
a[res] += 1
m = max(a)
r = [-1] * (m+1)
for i in range(TOP):
if r[a[i]]==-1: r[a[i]]=i
print(r)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Feb 25 2015
EXTENSIONS
More terms from Rémy Sigrist, Jul 14 2020
STATUS
approved