21815101 has 16 divisors (see below), whose sum is σ = 27577728. Its totient is φ = 16761600.

The previous prime is 21815099. The next prime is 21815107. The reversal of 21815101 is 10151812.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21815101 - 2¹ = 21815099 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 (21815107) 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, 3681 + ... + 7561.

It is an arithmetic number, because the mean of its divisors is an integer number (1723608).

Almost surely, 2^21815101 is an apocalyptic number.

It is an amenable number.

21815101 is a deficient number, since it is larger than the sum of its proper divisors (5762627).

21815101 is a wasteful number, since it uses less digits than its factorization.

21815101 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3972.

The product of its (nonzero) digits is 80, while the sum is 19.

The square root of 21815101 is about 4670.6638714427. The cubic root of 21815101 is about 279.4167322678.

Adding to 21815101 its reverse (10151812), we get a palindrome (31966913).

The spelling of 21815101 in words is "twenty-one million, eight hundred fifteen thousand, one hundred one".