666551556 has 144 divisors (see below), whose sum is σ = 1912135680. Its totient is φ = 194016960.

The previous prime is 666551551. The next prime is 666551591. The reversal of 666551556 is 655155666.

It is a super-2 number, since 2×666551556² = 888581953612042272, which contains 22 as substring.

It is a hoax number, since the sum of its digits (45) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (666551551) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1097805 + ... + 1098411.

It is an arithmetic number, because the mean of its divisors is an integer number (13278720).

Almost surely, 2^666551556 is an apocalyptic number.

666551556 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 666551556, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (956067840).

666551556 is an abundant number, since it is smaller than the sum of its proper divisors (1245584124).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

666551556 is a wasteful number, since it uses less digits than its factorization.

666551556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 734 (or 729 counting only the distinct ones).

The product of its digits is 810000, while the sum is 45.

The square root of 666551556 is about 25817.6597700101. The cubic root of 666551556 is about 873.5301826273.

The spelling of 666551556 in words is "six hundred sixty-six million, five hundred fifty-one thousand, five hundred fifty-six".