=LAMBDA(s,
    LET(
        ns, VLOOKUP(
            CHARS(s), CUSIPMAP, 2, FALSE
        ),

        AND(
            9 = COLUMNS(ns),
            LET(
                firstEight, INITCOLS(ns),

                ixs, SEQUENCE(1, 8),

                evensDoubled, IF(ISEVEN(ixs),
                    2 * INDEX(firstEight, 1, ixs),
                    INDEX(firstEight, 1, ixs)
                ),

                LASTCOL(ns) = MOD(
                    10 - MOD(
                        SUM(
                            QUOTIENT(evensDoubled, 10),
                            MOD(evensDoubled, 10)
                        ),
                        10
                    ),
                    10
                )
            )
        )
    )
)


CUSIPMAP
={"0",0;"1",1;"2",2;"3",3;"4",4;"5",5;"6",6;"7",7;"8",8;"9",9;"A",
10;"B",11;"C",12;"D",13;"E",14;"F",15;"G",16;"H",17;"I",18;"J",19;"K",
20;"L",21;"M",22;"N",23;"O",24;"P",25;"Q",26;"R",27;"S",28;"T",29;"U",
30;"V",31;"W",32;"X",33;"Y",34;"Z",35;"*",36;"@",37;"#",38}