Japan’s core inflation is seen slowing for a sixth month in January while factory output is expected to rise, underlining the policy challenge facing the Bank of Japan as it strives to speed up economic growth and achieve its 2 percent price target. Stripping out the effects of a sale tax hike, the nation’s core consumer price index (CPI) – excluding volatile fresh food but includes oil products – is forecast to have increased 0.3 percent year-on-year last month, a Reuters poll showed.