21400861561 has 4 divisors (see below), whose sum is σ = 21401165412. Its totient is φ = 21400557712.

The previous prime is 21400861541. The next prime is 21400861579. The reversal of 21400861561 is 16516800412.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 10245488400 + 11155373161 = 101220^2 + 105619^2 .

It is a cyclic number.

It is not a de Polignac number, because 21400861561 - 2⁵ = 21400861529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21400861541) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 14475 + ... + 207391.

It is an arithmetic number, because the mean of its divisors is an integer number (5350291353).

Almost surely, 2^21400861561 is an apocalyptic number.

It is an amenable number.

21400861561 is a deficient number, since it is larger than the sum of its proper divisors (303851).

21400861561 is a wasteful number, since it uses less digits than its factorization.

21400861561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 303850.

The product of its (nonzero) digits is 11520, while the sum is 34.

The spelling of 21400861561 in words is "twenty-one billion, four hundred million, eight hundred sixty-one thousand, five hundred sixty-one".