661620861 has 18 divisors (see below), whose sum is σ = 1050453950. Its totient is φ = 400981680.

The previous prime is 661620857. The next prime is 661620863. The reversal of 661620861 is 168026166.

It can be written as a sum of positive squares in only one way, i.e., 415915236 + 245705625 = 20394^2 + 15675^2 .

It is not a de Polignac number, because 661620861 - 2² = 661620857 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661620863) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 302686 + ... + 304863.

Almost surely, 2^661620861 is an apocalyptic number.

It is an amenable number.

661620861 is a deficient number, since it is larger than the sum of its proper divisors (388833089).

661620861 is a wasteful number, since it uses less digits than its factorization.

661620861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 607577 (or 607563 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 661620861 is about 25721.9917774654. The cubic root of 661620861 is about 871.3709222341.

The spelling of 661620861 in words is "six hundred sixty-one million, six hundred twenty thousand, eight hundred sixty-one".