The BIGINT or BIGSERIAL or INT8 or SERIAL8 data type can accept numbers with absolute values from 0 through 9,223,372,036,854,775,807 (plus or minus (2 to the 63rd power) - 1).
To store numbers that are outside this range, redefine the column or variable to use the DECIMAL data type. For more information on valid ranges of data types, see the IBM Informix Guide to SQL: Reference.