661155021 has 32 divisors (see below), whose sum is σ = 1017792000. Its totient is φ = 423670464.

The previous prime is 661155017. The next prime is 661155031. The reversal of 661155021 is 120551166.

It is a happy number.

It is not a de Polignac number, because 661155021 - 2² = 661155017 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661155031) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 185371 + ... + 188903.

It is an arithmetic number, because the mean of its divisors is an integer number (31806000).

Almost surely, 2^661155021 is an apocalyptic number.

It is an amenable number.

661155021 is a deficient number, since it is larger than the sum of its proper divisors (356636979).

661155021 is a wasteful number, since it uses less digits than its factorization.

661155021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3810 (or 3804 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 27.

The square root of 661155021 is about 25712.9348966624. The cubic root of 661155021 is about 871.1663666447.

The spelling of 661155021 in words is "six hundred sixty-one million, one hundred fifty-five thousand, twenty-one".