21505561786 has 16 divisors (see below), whose sum is σ = 32610614400. Its totient is φ = 10635607728.

The previous prime is 21505561771. The next prime is 21505561807. The reversal of 21505561786 is 68716550512.

21505561786 is digitally balanced in base 5, because in such base it contains all the possibile digits an equal number of times.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 110620 + ... + 235048.

It is an arithmetic number, because the mean of its divisors is an integer number (2038163400).

Almost surely, 2^21505561786 is an apocalyptic number.

21505561786 is a deficient number, since it is larger than the sum of its proper divisors (11105052614).

21505561786 is a wasteful number, since it uses less digits than its factorization.

21505561786 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125373.

The product of its (nonzero) digits is 504000, while the sum is 46.

The spelling of 21505561786 in words is "twenty-one billion, five hundred five million, five hundred sixty-one thousand, seven hundred eighty-six".