21205173942 has 24 divisors (see below), whose sum is σ = 45954891216. Its totient is φ = 7066799376.

The previous prime is 21205173931. The next prime is 21205173943. The reversal of 21205173942 is 24937150212.

21205173942 is a `hidden beast` number, since 212 + 0 + 51 + 7 + 394 + 2 = 666.

It is a junction number, because it is equal to n+sod(n) for n = 21205173897 and 21205173906.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205173943) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 49098 + ... + 211709.

It is an arithmetic number, because the mean of its divisors is an integer number (1914787134).

Almost surely, 2^21205173942 is an apocalyptic number.

21205173942 is an abundant number, since it is smaller than the sum of its proper divisors (24749717274).

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

21205173942 is a wasteful number, since it uses less digits than its factorization.

21205173942 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 265332 (or 265329 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 36.

The spelling of 21205173942 in words is "twenty-one billion, two hundred five million, one hundred seventy-three thousand, nine hundred forty-two".