21391212 has 24 divisors (see below), whose sum is σ = 51634800. Its totient is φ = 6884416.

The previous prime is 21391211. The next prime is 21391213. The reversal of 21391212 is 21219312.

It is an interprime number because it is at equal distance from previous prime (21391211) and next prime (21391213).

It is not an unprimeable number, because it can be changed into a prime (21391211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 30387 + ... + 31082.

It is an arithmetic number, because the mean of its divisors is an integer number (2151450).

Almost surely, 2^21391212 is an apocalyptic number.

It is an amenable number.

21391212 is an abundant number, since it is smaller than the sum of its proper divisors (30243588).

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

21391212 is a wasteful number, since it uses less digits than its factorization.

21391212 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 61505 (or 61503 counting only the distinct ones).

The product of its digits is 216, while the sum is 21.

The square root of 21391212 is about 4625.0634590241. The cubic root of 21391212 is about 277.5951009165.

The spelling of 21391212 in words is "twenty-one million, three hundred ninety-one thousand, two hundred twelve".