21415551 has 12 divisors (see below), whose sum is σ = 29172312. Its totient is φ = 13969488.

The previous prime is 21415547. The next prime is 21415561. The reversal of 21415551 is 15551412.

It is not a de Polignac number, because 21415551 - 2² = 21415547 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21415531) 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, 58170 + ... + 58536.

It is an arithmetic number, because the mean of its divisors is an integer number (2431026).

Almost surely, 2^21415551 is an apocalyptic number.

21415551 is a deficient number, since it is larger than the sum of its proper divisors (7756761).

21415551 is an frugal number, since it uses more digits than its factorization.

21415551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 790 (or 423 counting only the distinct ones).

The product of its digits is 1000, while the sum is 24.

The square root of 21415551 is about 4627.6939181411. The cubic root of 21415551 is about 277.7003439216.

Adding to 21415551 its reverse (15551412), we get a palindrome (36966963).

The spelling of 21415551 in words is "twenty-one million, four hundred fifteen thousand, five hundred fifty-one".