21215740 has 48 divisors (see below), whose sum is σ = 54839232. Its totient is φ = 6713856.

The previous prime is 21215693. The next prime is 21215759. The reversal of 21215740 is 4751212.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4009 + ... + 7648.

It is an arithmetic number, because the mean of its divisors is an integer number (1142484).

Almost surely, 2^21215740 is an apocalyptic number.

21215740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21215740 is an abundant number, since it is smaller than the sum of its proper divisors (33623492).

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

21215740 is a wasteful number, since it uses less digits than its factorization.

21215740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11686 (or 11684 counting only the distinct ones).

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21215740 is about 4606.0547109213. The cubic root of 21215740 is about 276.8339788942.

Adding to 21215740 its reverse (4751212), we get a palindrome (25966952).

The spelling of 21215740 in words is "twenty-one million, two hundred fifteen thousand, seven hundred forty".