21221520 has 40 divisors (see below), whose sum is σ = 65787456. Its totient is φ = 5659008.

The previous prime is 21221509. The next prime is 21221521. The reversal of 21221520 is 2512212.

It is a tau number, because it is divible by the number of its divisors (40).

It is a super-2 number, since 2×21221520² = 900705822220800, which contains 22 as substring.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21221520.

It is not an unprimeable number, because it can be changed into a prime (21221521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 43972 + ... + 44451.

Almost surely, 2^21221520 is an apocalyptic number.

21221520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21221520 is an abundant number, since it is smaller than the sum of its proper divisors (44565936).

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

21221520 is a wasteful number, since it uses less digits than its factorization.

21221520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88439 (or 88433 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21221520 is about 4606.6821032062. The cubic root of 21221520 is about 276.8591167574.

Adding to 21221520 its reverse (2512212), we get a palindrome (23733732).

The spelling of 21221520 in words is "twenty-one million, two hundred twenty-one thousand, five hundred twenty".