661489920 has 432 divisors, whose sum is σ = 2821308672. Its totient is φ = 139345920.

The previous prime is 661489901. The next prime is 661489951. The reversal of 661489920 is 29984166.

It is a happy number.

661489920 is a `hidden beast` number, since 6 + 614 + 8 + 9 + 9 + 20 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1048005 + ... + 1048635.

Almost surely, 2^661489920 is an apocalyptic number.

661489920 is a gapful number since it is divisible by the number (60) 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 661489920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1410654336).

661489920 is an abundant number, since it is smaller than the sum of its proper divisors (2159818752).

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

661489920 is a wasteful number, since it uses less digits than its factorization.

661489920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 678 (or 661 counting only the distinct ones).

The product of its (nonzero) digits is 186624, while the sum is 45.

The square root of 661489920 is about 25719.4463392974. The cubic root of 661489920 is about 871.3134342706.

The spelling of 661489920 in words is "six hundred sixty-one million, four hundred eighty-nine thousand, nine hundred twenty".