21218761 has 8 divisors (see below), whose sum is σ = 21734784. Its totient is φ = 20705520.

The previous prime is 21218759. The next prime is 21218777. The reversal of 21218761 is 16781212.

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 21218761 - 2¹ = 21218759 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 (21218741) 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, 30726 + ... + 31408.

It is an arithmetic number, because the mean of its divisors is an integer number (2716848).

Almost surely, 2^21218761 is an apocalyptic number.

It is an amenable number.

21218761 is a deficient number, since it is larger than the sum of its proper divisors (516023).

21218761 is an equidigital number, since it uses as much as digits as its factorization.

21218761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1391.

The product of its digits is 1344, while the sum is 28.

The square root of 21218761 is about 4606.3826371677. The cubic root of 21218761 is about 276.8471181288.

Adding to 21218761 its reverse (16781212), we get a palindrome (37999973).

The spelling of 21218761 in words is "twenty-one million, two hundred eighteen thousand, seven hundred sixty-one".