21521403 has 16 divisors (see below), whose sum is σ = 32092960. Its totient is φ = 14253408.

The previous prime is 21521389. The next prime is 21521413. The reversal of 21521403 is 30412512.

It is not a de Polignac number, because 21521403 - 2⁴ = 21521387 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521413) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1701 + ... + 6777.

It is an arithmetic number, because the mean of its divisors is an integer number (2005810).

Almost surely, 2^21521403 is an apocalyptic number.

21521403 is a deficient number, since it is larger than the sum of its proper divisors (10571557).

21521403 is a wasteful number, since it uses less digits than its factorization.

21521403 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5243 (or 5237 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21521403 is about 4639.1166184954. The cubic root of 21521403 is about 278.1571278460.

Adding to 21521403 its reverse (30412512), we get a palindrome (51933915).

The spelling of 21521403 in words is "twenty-one million, five hundred twenty-one thousand, four hundred three".