21507925517 has 4 divisors (see below), whose sum is σ = 23162381340. Its totient is φ = 19853469696.

The previous prime is 21507925507. The next prime is 21507925561. The reversal of 21507925517 is 71552970512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13150126276 + 8357799241 = 114674^2 + 91421^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21507925517 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 (21507925507) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 827227892 + ... + 827227917.

It is an arithmetic number, because the mean of its divisors is an integer number (5790595335).

Almost surely, 2^21507925517 is an apocalyptic number.

It is an amenable number.

21507925517 is a deficient number, since it is larger than the sum of its proper divisors (1654455823).

21507925517 is a wasteful number, since it uses less digits than its factorization.

21507925517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1654455822.

The product of its (nonzero) digits is 220500, while the sum is 44.

The spelling of 21507925517 in words is "twenty-one billion, five hundred seven million, nine hundred twenty-five thousand, five hundred seventeen".