21025215517 has 8 divisors (see below), whose sum is σ = 21540312576. Its totient is φ = 20512941552.

The previous prime is 21025215493. The next prime is 21025215569. The reversal of 21025215517 is 71551252012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21025215517 - 2²⁷ = 20890997789 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 (21025215017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 690693 + ... + 720490.

It is an arithmetic number, because the mean of its divisors is an integer number (2692539072).

Almost surely, 2^21025215517 is an apocalyptic number.

It is an amenable number.

21025215517 is a deficient number, since it is larger than the sum of its proper divisors (515097059).

21025215517 is a wasteful number, since it uses less digits than its factorization.

21025215517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1411547.

The product of its (nonzero) digits is 7000, while the sum is 31.

Adding to 21025215517 its reverse (71551252012), we get a palindrome (92576467529).

The spelling of 21025215517 in words is "twenty-one billion, twenty-five million, two hundred fifteen thousand, five hundred seventeen".