21197561 has 16 divisors (see below), whose sum is σ = 26867328. Its totient is φ = 16243200.

The previous prime is 21197551. The next prime is 21197563. The reversal of 21197561 is 16579112.

It is a cyclic number.

It is not a de Polignac number, because 21197561 - 2¹⁸ = 20935417 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21197563) 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, 2441 + ... + 6953.

It is an arithmetic number, because the mean of its divisors is an integer number (1679208).

Almost surely, 2^21197561 is an apocalyptic number.

It is an amenable number.

21197561 is a deficient number, since it is larger than the sum of its proper divisors (5669767).

21197561 is a wasteful number, since it uses less digits than its factorization.

21197561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4592.

The product of its digits is 3780, while the sum is 32.

The square root of 21197561 is about 4604.0809071953. The cubic root of 21197561 is about 276.7548866260.

The spelling of 21197561 in words is "twenty-one million, one hundred ninety-seven thousand, five hundred sixty-one".