21091020 has 24 divisors (see below), whose sum is σ = 59055024. Its totient is φ = 5624256.

The previous prime is 21091009. The next prime is 21091051. The reversal of 21091020 is 2019012.

It is a happy number.

It is a super-2 number, since 2×21091020² = 889662249280800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 175699 + ... + 175818.

It is an arithmetic number, because the mean of its divisors is an integer number (2460626).

Almost surely, 2^21091020 is an apocalyptic number.

21091020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21091020 is an abundant number, since it is smaller than the sum of its proper divisors (37964004).

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

21091020 is a wasteful number, since it uses less digits than its factorization.

21091020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 351529 (or 351527 counting only the distinct ones).

The product of its (nonzero) digits is 36, while the sum is 15.

The square root of 21091020 is about 4592.4960533462. The cubic root of 21091020 is about 276.2904419952.

The spelling of 21091020 in words is "twenty-one million, ninety-one thousand, twenty".