21420810 has 24 divisors (see below), whose sum is σ = 55694340. Its totient is φ = 5712192.

The previous prime is 21420793. The next prime is 21420811. The reversal of 21420810 is 1802412.

It can be written as a sum of positive squares in 2 ways, for example, as 19900521 + 1520289 = 4461^2 + 1233^2 .

It is a super-2 number, since 2×21420810² = 917702202112200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21420811) 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, 118915 + ... + 119094.

Almost surely, 2^21420810 is an apocalyptic number.

21420810 is an abundant number, since it is smaller than the sum of its proper divisors (34273530).

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

21420810 is a wasteful number, since it uses less digits than its factorization.

21420810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 238022 (or 238019 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21420810 is about 4628.2620928379. The cubic root of 21420810 is about 277.7230736127.

The spelling of 21420810 in words is "twenty-one million, four hundred twenty thousand, eight hundred ten".