21615245 has 16 divisors (see below), whose sum is σ = 27727920. Its totient is φ = 16118784.

The previous prime is 21615233. The next prime is 21615247. The reversal of 21615245 is 54251612.

It can be written as a sum of positive squares in 8 ways, for example, as 206116 + 21409129 = 454^2 + 4627^2 .

It is a cyclic number.

It is not a de Polignac number, because 21615245 - 2⁴ = 21615229 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21615247) 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, 8099 + ... + 10431.

It is an arithmetic number, because the mean of its divisors is an integer number (1732995).

Almost surely, 2^21615245 is an apocalyptic number.

It is an amenable number.

21615245 is a deficient number, since it is larger than the sum of its proper divisors (6112675).

21615245 is a wasteful number, since it uses less digits than its factorization.

21615245 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2464.

The product of its digits is 2400, while the sum is 26.

The square root of 21615245 is about 4649.2198270247. The cubic root of 21615245 is about 278.5608340731.

Adding to 21615245 its reverse (54251612), we get a palindrome (75866857).

The spelling of 21615245 in words is "twenty-one million, six hundred fifteen thousand, two hundred forty-five".