OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Biquadratic Number
EXAMPLE
259 = 1^4 + 1^4 + 1^4 + 4^4 = 2^4 + 3^4 + 3^4 + 3^4, so 259 is in the sequence.
MAPLE
N:= 10^5: # for terms <= N
V:= Vector(N, datatype=integer[4]):
for a from 1 while a^4 <= N do
for b from 1 to a while a^4+b^4 <= N do
for c from 1 to b while a^4 + b^4+ c^4 <= N do
for d from 1 to c do
v:= a^4+b^4+c^4+d^4;
if v > N then break fi;
V[v]:= V[v]+1
od od od od:
select(i -> V[i]>1, [$1..N]); # Robert Israel, Oct 07 2019
MATHEMATICA
Select[Range@20000, Length@Select[PowersRepresentations[#, 4, 4], ! MemberQ[#, 0] &] > 1 &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Aug 15 2019
STATUS
approved