661956921 has 16 divisors (see below), whose sum is σ = 1003485120. Its totient is φ = 431040960.

The previous prime is 661956887. The next prime is 661956923. The reversal of 661956921 is 129659166.

It is a happy number.

661956921 is a `hidden beast` number, since 6 + 61 + 9 + 569 + 21 = 666.

It is not a de Polignac number, because 661956921 - 2⁷ = 661956793 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661956923) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 283920 + ... + 286241.

It is an arithmetic number, because the mean of its divisors is an integer number (62717820).

Almost surely, 2^661956921 is an apocalyptic number.

It is an amenable number.

661956921 is a deficient number, since it is larger than the sum of its proper divisors (341528199).

661956921 is a wasteful number, since it uses less digits than its factorization.

661956921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 570213 (or 570207 counting only the distinct ones).

The product of its digits is 174960, while the sum is 45.

The square root of 661956921 is about 25728.5234904765. The cubic root of 661956921 is about 871.5184303531.

The spelling of 661956921 in words is "six hundred sixty-one million, nine hundred fifty-six thousand, nine hundred twenty-one".