21025515 has 32 divisors (see below), whose sum is σ = 40711680. Its totient is φ = 9045504.

The previous prime is 21025513. The next prime is 21025561. The reversal of 21025515 is 51552012.

It is not a de Polignac number, because 21025515 - 2¹ = 21025513 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a junction number, because it is equal to n+sod(n) for n = 21025491 and 21025500.

It is not an unprimeable number, because it can be changed into a prime (21025513) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4105 + ... + 7674.

It is an arithmetic number, because the mean of its divisors is an integer number (1272240).

Almost surely, 2^21025515 is an apocalyptic number.

21025515 is a deficient number, since it is larger than the sum of its proper divisors (19686165).

21025515 is a wasteful number, since it uses less digits than its factorization.

21025515 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11811.

The product of its (nonzero) digits is 500, while the sum is 21.

The square root of 21025515 is about 4585.3587645897. The cubic root of 21025515 is about 276.0041088445.

Adding to 21025515 its reverse (51552012), we get a palindrome (72577527).

The spelling of 21025515 in words is "twenty-one million, twenty-five thousand, five hundred fifteen".