21256020610566 has 32 divisors (see below), whose sum is σ = 48586980176640. Its totient is φ = 6072924969696.

The previous prime is 21256020610441. The next prime is 21256020610597. The reversal of 21256020610566 is 66501602065212.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8168901 + ... + 10451936.

It is an arithmetic number, because the mean of its divisors is an integer number (1518343130520).

Almost surely, 2^{21256020610566} is an apocalyptic number.

21256020610566 is an abundant number, since it is smaller than the sum of its proper divisors (27330959566074).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21256020610566 is a wasteful number, since it uses less digits than its factorization.

21256020610566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18648028.

The product of its (nonzero) digits is 259200, while the sum is 42.

Adding to 21256020610566 its reverse (66501602065212), we get a palindrome (87757622675778).

The spelling of 21256020610566 in words is "twenty-one trillion, two hundred fifty-six billion, twenty million, six hundred ten thousand, five hundred sixty-six".