21312220 has 24 divisors (see below), whose sum is σ = 47389104. Its totient is φ = 8023296.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312220 is 2221312.

It is a self number, because there is not a number n which added to its sum of digits gives 21312220.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312223) 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, 31002 + ... + 31681.

It is an arithmetic number, because the mean of its divisors is an integer number (1974546).

Almost surely, 2^21312220 is an apocalyptic number.

21312220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21312220 is an abundant number, since it is smaller than the sum of its proper divisors (26076884).

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

21312220 is a wasteful number, since it uses less digits than its factorization.

21312220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62709 (or 62707 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21312220 is about 4616.5160023550. The cubic root of 21312220 is about 277.2529847417.

Adding to 21312220 its reverse (2221312), we get a palindrome (23533532).

The spelling of 21312220 in words is "twenty-one million, three hundred twelve thousand, two hundred twenty".