21365665020 has 108 divisors (see below), whose sum is σ = 75390306264. Its totient is φ = 4883578560.

The previous prime is 21365665019. The next prime is 21365665043. The reversal of 21365665020 is 2056656312.

It is a happy number.

21365665020 is a `hidden beast` number, since 21 + 3 + 6 + 566 + 50 + 20 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 1202386 + ... + 1220025.

Almost surely, 2^21365665020 is an apocalyptic number.

21365665020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21365665020 is an abundant number, since it is smaller than the sum of its proper divisors (54024641244).

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

21365665020 is a wasteful number, since it uses less digits than its factorization.

21365665020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2422440 (or 2422428 counting only the distinct ones).

The product of its (nonzero) digits is 64800, while the sum is 36.

The spelling of 21365665020 in words is "twenty-one billion, three hundred sixty-five million, six hundred sixty-five thousand, twenty".