Twice linear

def dbl_linear(n):
result = [1]
X = 0
Y = 0
i = 0
while i < n:
XX = result[X] * 2 +1
YY = result[Y] * 3 +1
i+=1
if XX < YY:
result.append(XX)
X += 1
elif XX == YY:
X+=1
Y+=1
result.append(XX)
else:
result.append(YY)
Y+=1

print(result)
return result[-1]