21561167555778 has 32 divisors (see below), whose sum is σ = 43412486544000. Its totient is φ = 7138698924416.

The previous prime is 21561167555729. The next prime is 21561167555791. The reversal of 21561167555778 is 87755576116512.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 63231550 + ... + 63571622.

It is an arithmetic number, because the mean of its divisors is an integer number (1356640204500).

Almost surely, 2^{21561167555778} is an apocalyptic number.

21561167555778 is an abundant number, since it is smaller than the sum of its proper divisors (21851318988222).

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

21561167555778 is a wasteful number, since it uses less digits than its factorization.

21561167555778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 411146.

The product of its digits is 123480000, while the sum is 66.

The spelling of 21561167555778 in words is "twenty-one trillion, five hundred sixty-one billion, one hundred sixty-seven million, five hundred fifty-five thousand, seven hundred seventy-eight".