21406553 has 16 divisors (see below), whose sum is σ = 26801280. Its totient is φ = 16670976.

The previous prime is 21406549. The next prime is 21406589. The reversal of 21406553 is 35560412.

It is not a de Polignac number, because 21406553 - 2² = 21406549 is a prime.

It is a super-2 number, since 2×21406553² = 916481022683618, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21406543) 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, 350 + ... + 6552.

It is an arithmetic number, because the mean of its divisors is an integer number (1675080).

Almost surely, 2^21406553 is an apocalyptic number.

It is an amenable number.

21406553 is a deficient number, since it is larger than the sum of its proper divisors (5394727).

21406553 is a wasteful number, since it uses less digits than its factorization.

21406553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6256.

The product of its (nonzero) digits is 3600, while the sum is 26.

The square root of 21406553 is about 4626.7216255141. The cubic root of 21406553 is about 277.6614454324.

Adding to 21406553 its reverse (35560412), we get a palindrome (56966965).

The spelling of 21406553 in words is "twenty-one million, four hundred six thousand, five hundred fifty-three".