21005647890 has 32 divisors (see below), whose sum is σ = 50704975296. Its totient is φ = 5569126080.

The previous prime is 21005647849. The next prime is 21005647919. The reversal of 21005647890 is 9874650012.

It is a super-2 number, since 2×21005647890² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2018476 + ... + 2028855.

It is an arithmetic number, because the mean of its divisors is an integer number (1584530478).

Almost surely, 2^21005647890 is an apocalyptic number.

21005647890 is an abundant number, since it is smaller than the sum of its proper divisors (29699327406).

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

21005647890 is a wasteful number, since it uses less digits than its factorization.

21005647890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4047514.

The product of its (nonzero) digits is 120960, while the sum is 42.

The spelling of 21005647890 in words is "twenty-one billion, five million, six hundred forty-seven thousand, eight hundred ninety".