21634561 has 8 divisors (see below), whose sum is σ = 23335424. Its totient is φ = 19938960.

The previous prime is 21634549. The next prime is 21634573. The reversal of 21634561 is 16543612.

It is an interprime number because it is at equal distance from previous prime (21634549) and next prime (21634573).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21634561 - 2⁷ = 21634433 is a prime.

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

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21634541) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13366 + ... + 14896.

It is an arithmetic number, because the mean of its divisors is an integer number (2916928).

Almost surely, 2^21634561 is an apocalyptic number.

It is an amenable number.

21634561 is a deficient number, since it is larger than the sum of its proper divisors (1700863).

21634561 is a wasteful number, since it uses less digits than its factorization.

21634561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2631.

The product of its digits is 4320, while the sum is 28.

The square root of 21634561 is about 4651.2967009212. The cubic root of 21634561 is about 278.6437860065.

It can be divided in two parts, 2163 and 4561, that added together give a square (6724 = 82²).

The spelling of 21634561 in words is "twenty-one million, six hundred thirty-four thousand, five hundred sixty-one".