21418781 has 4 divisors (see below), whose sum is σ = 21456864. Its totient is φ = 21380700.

The previous prime is 21418777. The next prime is 21418801. The reversal of 21418781 is 18781412.

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 21418781 - 2² = 21418777 is a prime.

It is a super-2 number, since 2×21418781² = 917528359051922, which contains 22 as substring.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21418741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18185 + ... + 19326.

It is an arithmetic number, because the mean of its divisors is an integer number (5364216).

Almost surely, 2^21418781 is an apocalyptic number.

It is an amenable number.

21418781 is a deficient number, since it is larger than the sum of its proper divisors (38083).

21418781 is an equidigital number, since it uses as much as digits as its factorization.

21418781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38082.

The product of its digits is 3584, while the sum is 32.

The square root of 21418781 is about 4628.0428908989. The cubic root of 21418781 is about 277.7143046025.

The spelling of 21418781 in words is "twenty-one million, four hundred eighteen thousand, seven hundred eighty-one".