OFFSET
0,2
EXAMPLE
a(3) = 561 since 176 = (8*4+1)*(8*2+1) = (10*5+1)*(10*1+1) = (16*2+1)*(16*1+1) is the first number that can be obtained in exactly 3 ways.
MAPLE
N:= 10^8:
V:= Vector(N, datatype=integer[4]):
for x from 3 while (2*x+1)*(x+1) <= N do
for y from 2 to x-1 while (x*y+1)*(x+1) <= N do
for z from 1 to y-1 do
v:= (x*y+1)*(x*z+1);
if v > N then break fi;
V[v]:= V[v]+1;
od od od:
R:= Array(0..26):
for j from 1 to N do
v:= V[j]; if R[v] = 0 then R[v]:= j fi
od:
convert(R[0..24], list);
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Jun 10 2021
STATUS
approved