Try it:
SELECT SUM(P.ITEMAMOUNT) AS AMOUNT, P.COMPANYID AS COMPANY, SUBSTR(P.ACCOUNTID, 1,5) AS ACCOUNT
FROM PRODUCTS P INNER JOIN ACCOUNTS A ON P.COMPANY = A.COMPANY AND P.ACCOUNTID = A.ACCOUNTID
WHERE P.ACCOUNTID LIKE '1%'
GROUP BY P.COMPANY, SUBSTR(P.ACCOUNTID, 1,5)
ORDER BY P.COMPANY, SUBSTR(P.ACCOUNTID, 1,5)