21213550 has 12 divisors (see below), whose sum is σ = 39457296. Its totient is φ = 8485400.

The previous prime is 21213487. The next prime is 21213553. The reversal of 21213550 is 5531212.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213553) 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 5 ways as a sum of consecutive naturals, for example, 212086 + ... + 212185.

It is an arithmetic number, because the mean of its divisors is an integer number (3288108).

Almost surely, 2^21213550 is an apocalyptic number.

21213550 is a deficient number, since it is larger than the sum of its proper divisors (18243746).

21213550 is a wasteful number, since it uses less digits than its factorization.

21213550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 424283 (or 424278 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 19.

The square root of 21213550 is about 4605.8169742186. The cubic root of 21213550 is about 276.8244531478.

Adding to 21213550 its reverse (5531212), we get a palindrome (26744762).

It can be divided in two parts, 2121 and 3550, that added together give a triangular number (5671 = T₁₀₆).

The spelling of 21213550 in words is "twenty-one million, two hundred thirteen thousand, five hundred fifty".