OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1) = 145 = 2^2 + 5^3 + 2^4 = 11^2 + 2^3 + 2^4 .
The first term which can be written in three different ways is
17367 = 23^2 + 13^3 + 11^4 = 113^2 + 13^3 + 7^4 = 131^2 + 5^3 + 3^4 .
MAPLE
N:= 10^5: # to get terms <= N
P:= select(isprime, [2, seq(i, i=3..floor(sqrt(N)))]):
Psq:= map(`^`, P, 2):
P3:= select(`<=`, map(`^`, P, 3), N):
P4:= select(`<=`, map(`^`, P, 4), N):
V:= Vector(N):
for a in Psq do for b in P3 do for c in P4 do
s:= a+b+c;
if s <= N then V[s]:= V[s]+1 fi
od od od:
select(t -> V[t]>=2, [$1..N]); # Robert Israel, Jan 30 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Philippe Guglielmetti, Aug 28 2018
STATUS
approved