661521020 has 12 divisors (see below), whose sum is σ = 1389194184. Its totient is φ = 264608400.

The previous prime is 661520999. The next prime is 661521031. The reversal of 661521020 is 20125166.

661521020 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a super-2 number, since 2×661521020² = 875220119803680800, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16538006 + ... + 16538045.

It is an arithmetic number, because the mean of its divisors is an integer number (115766182).

Almost surely, 2^661521020 is an apocalyptic number.

It is an amenable number.

661521020 is an abundant number, since it is smaller than the sum of its proper divisors (727673164).

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

661521020 is a wasteful number, since it uses less digits than its factorization.

661521020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33076060 (or 33076058 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 661521020 is about 25720.0509330755. The cubic root of 661521020 is about 871.3270890129.

Adding to 661521020 its reverse (20125166), we get a palindrome (681646186).

The spelling of 661521020 in words is "six hundred sixty-one million, five hundred twenty-one thousand, twenty".