21618761 has 4 divisors (see below), whose sum is σ = 21879312. Its totient is φ = 21358212.

The previous prime is 21618739. The next prime is 21618787. The reversal of 21618761 is 16781612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21618761 - 2⁶ = 21618697 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 (21618661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 130151 + ... + 130316.

It is an arithmetic number, because the mean of its divisors is an integer number (5469828).

Almost surely, 2^21618761 is an apocalyptic number.

It is an amenable number.

21618761 is a deficient number, since it is larger than the sum of its proper divisors (260551).

21618761 is an equidigital number, since it uses as much as digits as its factorization.

21618761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 260550.

The product of its digits is 4032, while the sum is 32.

The square root of 21618761 is about 4649.5979396073. The cubic root of 21618761 is about 278.5759370987.

The spelling of 21618761 in words is "twenty-one million, six hundred eighteen thousand, seven hundred sixty-one".