21096781 has 4 divisors (see below), whose sum is σ = 21385852. Its totient is φ = 20807712.

The previous prime is 21096763. The next prime is 21096787. The reversal of 21096781 is 18769012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15015625 + 6081156 = 3875^2 + 2466^2 .

It is a cyclic number.

It is not a de Polignac number, because 21096781 - 2⁷ = 21096653 is a prime.

It is a super-2 number, since 2×21096781² = 890148337123922, 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 (21096787) 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, 144426 + ... + 144571.

It is an arithmetic number, because the mean of its divisors is an integer number (5346463).

Almost surely, 2^21096781 is an apocalyptic number.

It is an amenable number.

21096781 is a deficient number, since it is larger than the sum of its proper divisors (289071).

21096781 is an equidigital number, since it uses as much as digits as its factorization.

21096781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 289070.

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 21096781 is about 4593.1232293506. The cubic root of 21096781 is about 276.3155958969.

The spelling of 21096781 in words is "twenty-one million, ninety-six thousand, seven hundred eighty-one".