21097169561 has 16 divisors (see below), whose sum is σ = 23108334480. Its totient is φ = 19144012800.

The previous prime is 21097169539. The next prime is 21097169573. The reversal of 21097169561 is 16596179012.

It can be written as a sum of positive squares in 8 ways, for example, as 4670902336 + 16426267225 = 68344^2 + 128165^2 .

It is a cyclic number.

It is not a de Polignac number, because 21097169561 - 2²² = 21092975257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21097169501) 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, 147461 + ... + 252861.

It is an arithmetic number, because the mean of its divisors is an integer number (1444270905).

Almost surely, 2^21097169561 is an apocalyptic number.

It is an amenable number.

21097169561 is a deficient number, since it is larger than the sum of its proper divisors (2011164919).

21097169561 is a wasteful number, since it uses less digits than its factorization.

21097169561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 105676.

The product of its (nonzero) digits is 204120, while the sum is 47.

The spelling of 21097169561 in words is "twenty-one billion, ninety-seven million, one hundred sixty-nine thousand, five hundred sixty-one".