21218477 has 16 divisors (see below), whose sum is σ = 25193472. Its totient is φ = 17487360.

The previous prime is 21218473. The next prime is 21218503. The reversal of 21218477 is 77481212.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21218477 - 2² = 21218473 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218473) 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, 59933 + ... + 60285.

It is an arithmetic number, because the mean of its divisors is an integer number (1574592).

Almost surely, 2^21218477 is an apocalyptic number.

It is an amenable number.

21218477 is a deficient number, since it is larger than the sum of its proper divisors (3974995).

21218477 is a wasteful number, since it uses less digits than its factorization.

21218477 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 668.

The product of its digits is 6272, while the sum is 32.

The square root of 21218477 is about 4606.3518102724. The cubic root of 21218477 is about 276.8458829808.

Adding to 21218477 its reverse (77481212), we get a palindrome (98699689).

The spelling of 21218477 in words is "twenty-one million, two hundred eighteen thousand, four hundred seventy-seven".