/* Predicate function that checks wether an integer is a Giuga number or not */
giugap(n):=if not primep(n) then block(ifactors(n),map(lambda([x],mod((n/x)-1,x)=0),map(first,%%)),
    if length(unique(%%))=1 and apply(lhs,unique(%%))=0 then true)$

/* Function that returns a list of the first len Giuga integers */
giuga_count(len):=block(
    [i:1,count:0,result:[]],
    while count<len do (if giugap(i) then (result:endcons(i,result),count:count+1),i:i+1),
    result)$

/* Test case */
giuga_count(4);