21618961 has 8 divisors (see below), whose sum is σ = 26608064. Its totient is φ = 17105040.

The previous prime is 21618959. The next prime is 21618967. The reversal of 21618961 is 16981612.

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 21618961 - 2¹ = 21618959 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 (21618967) 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, 118695 + ... + 118876.

It is an arithmetic number, because the mean of its divisors is an integer number (3326008).

Almost surely, 2^21618961 is an apocalyptic number.

It is an amenable number.

21618961 is a deficient number, since it is larger than the sum of its proper divisors (4989103).

21618961 is a wasteful number, since it uses less digits than its factorization.

21618961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 237591.

The product of its digits is 5184, while the sum is 34.

The square root of 21618961 is about 4649.6194467935. The cubic root of 21618961 is about 278.5767961522.

The spelling of 21618961 in words is "twenty-one million, six hundred eighteen thousand, nine hundred sixty-one".