21643210 has 24 divisors (see below), whose sum is σ = 41389740. Its totient is φ = 8146944.

The previous prime is 21643201. The next prime is 21643217. The reversal of 21643210 is 1234612.

It can be written as a sum of positive squares in 6 ways, for example, as 15547249 + 6095961 = 3943^2 + 2469^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21643217) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 855 + ... + 6634.

Almost surely, 2^21643210 is an apocalyptic number.

21643210 is a deficient number, since it is larger than the sum of its proper divisors (19746530).

21643210 is a wasteful number, since it uses less digits than its factorization.

21643210 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7530 (or 7513 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21643210 is about 4652.2263487496. The cubic root of 21643210 is about 278.6809128522.

Adding to 21643210 its reverse (1234612), we get a palindrome (22877822).

It can be divided in two parts, 216 and 43210, that multiplied together give a triangular number (9333360 = T₄₃₂₀).

The spelling of 21643210 in words is "twenty-one million, six hundred forty-three thousand, two hundred ten".