661056021 has 24 divisors (see below), whose sum is σ = 962017056. Its totient is φ = 437415840.

The previous prime is 661056013. The next prime is 661056029. The reversal of 661056021 is 120650166.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (661056013) and next prime (661056029).

It is not a de Polignac number, because 661056021 - 2³ = 661056013 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661056029) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1173886 + ... + 1174448.

It is an arithmetic number, because the mean of its divisors is an integer number (40084044).

Almost surely, 2^661056021 is an apocalyptic number.

It is an amenable number.

661056021 is a deficient number, since it is larger than the sum of its proper divisors (300961035).

661056021 is a wasteful number, since it uses less digits than its factorization.

661056021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1313 (or 1310 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 661056021 is about 25711.0097234628. The cubic root of 661056021 is about 871.1228822512.

The spelling of 661056021 in words is "six hundred sixty-one million, fifty-six thousand, twenty-one".