21232561 has 16 divisors (see below), whose sum is σ = 25285504. Its totient is φ = 17449344.

The previous prime is 21232531. The next prime is 21232571. The reversal of 21232561 is 16523212.

It is a cyclic number.

It is not a de Polignac number, because 21232561 - 2⁹ = 21232049 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21232511) 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, 18346 + ... + 19468.

It is an arithmetic number, because the mean of its divisors is an integer number (1580344).

Almost surely, 2^21232561 is an apocalyptic number.

It is an amenable number.

21232561 is a deficient number, since it is larger than the sum of its proper divisors (4052943).

21232561 is a wasteful number, since it uses less digits than its factorization.

21232561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1240.

The product of its digits is 720, while the sum is 22.

The square root of 21232561 is about 4607.8803152860. The cubic root of 21232561 is about 276.9071226108.

Adding to 21232561 its reverse (16523212), we get a palindrome (37755773).

The spelling of 21232561 in words is "twenty-one million, two hundred thirty-two thousand, five hundred sixty-one".