OFFSET
1,3
COMMENTS
Record values of A137401: 0, 2, 7, 12, 20, 63, 116, 131, 182, 339, 602, 839, 1808, 3311, 4328, 7964, 8864, 9231, 19583, 21986, 41363, 52676, 81467, 87596, 92087, 112616, 236951, 247940, 378071, 386423, 521135, ... - Robert G. Wilson v
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10000 (terms n = 1..425 from Robert G. Wilson v)
FORMULA
EXAMPLE
a(4)=7 because (1, 2, 1), (1, 3, 2), (2, 1, 1), (2, 2, 2), (2, 3, 3), (3, 1, 2), (3, 2, 3) are solutions for n=4.
MATHEMATICA
f[n_] := Block[ {c = 0}, Do[ If[ Mod[x^3 + y^3, n] == Mod[z^3, n], c++ ], {x, n - 1}, {y, n - 1}, {z, n - 1}]; c];
Table[Length[Select[Tuples[Range[n - 1], 3], Mod[ #[[1]]^3 + #[[2]]^3 - #[[3]]^3, n] == 0 &]], {n, 2, 50}] (* Stefan Steinerberger, Apr 12 2008 *)
PROG
(Python)
def A137401(n):
ndict = {}
for i in range(1, n):
m = pow(i, 3, n)
if m in ndict:
ndict[m] += 1
else:
ndict[m] = 1
count = 0
for i in ndict:
ni = ndict[i]
for j in ndict:
k = (i+j) % n
if k in ndict:
count += ni*ndict[j]*ndict[k]
return count # Chai Wah Wu, Jun 06 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Neven Juric (neven.juric(AT)apis-it.hr), Apr 11 2008
EXTENSIONS
More terms from Stefan Steinerberger and Robert G. Wilson v, Apr 12 2008
STATUS
approved