21087581561 has 16 divisors (see below), whose sum is σ = 21637031040. Its totient is φ = 20546520960.

The previous prime is 21087581497. The next prime is 21087581563. The reversal of 21087581561 is 16518578012.

It is a cyclic number.

It is not a de Polignac number, because 21087581561 - 2⁶ = 21087581497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21087581563) 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, 2222750 + ... + 2232216.

It is an arithmetic number, because the mean of its divisors is an integer number (1352314440).

Almost surely, 2^21087581561 is an apocalyptic number.

It is an amenable number.

21087581561 is a deficient number, since it is larger than the sum of its proper divisors (549449479).

21087581561 is a wasteful number, since it uses less digits than its factorization.

21087581561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9904.

The product of its (nonzero) digits is 134400, while the sum is 44.

The spelling of 21087581561 in words is "twenty-one billion, eighty-seven million, five hundred eighty-one thousand, five hundred sixty-one".