21540402 has 72 divisors (see below), whose sum is σ = 51757524. Its totient is φ = 6469632.

The previous prime is 21540383. The next prime is 21540437. The reversal of 21540402 is 20404512.

It can be written as a sum of positive squares in 6 ways, for example, as 3316041 + 18224361 = 1821^2 + 4269^2 .

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

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 222018 + ... + 222114.

Almost surely, 2^21540402 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21540402, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25878762).

21540402 is an abundant number, since it is smaller than the sum of its proper divisors (30217122).

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

21540402 is a wasteful number, since it uses less digits than its factorization.

21540402 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 204 (or 188 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21540402 is about 4641.1638626534. The cubic root of 21540402 is about 278.2389557351.

Adding to 21540402 its reverse (20404512), we get a palindrome (41944914).

The spelling of 21540402 in words is "twenty-one million, five hundred forty thousand, four hundred two".