21505510561 has 32 divisors (see below), whose sum is σ = 23412533760. Its totient is φ = 19678982400.

The previous prime is 21505510489. The next prime is 21505510573. The reversal of 21505510561 is 16501550512.

It is not a de Polignac number, because 21505510561 - 2²³ = 21497121953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21505516561) 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, 64971166 + ... + 64971496.

It is an arithmetic number, because the mean of its divisors is an integer number (731641680).

Almost surely, 2^21505510561 is an apocalyptic number.

It is an amenable number.

21505510561 is a deficient number, since it is larger than the sum of its proper divisors (1907023199).

21505510561 is a wasteful number, since it uses less digits than its factorization.

21505510561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 925.

The product of its (nonzero) digits is 7500, while the sum is 31.

The spelling of 21505510561 in words is "twenty-one billion, five hundred five million, five hundred ten thousand, five hundred sixty-one".