21116781 has 20 divisors (see below), whose sum is σ = 36052192. Its totient is φ = 12066408.

The previous prime is 21116773. The next prime is 21116801. The reversal of 21116781 is 18761112.

It is not a de Polignac number, because 21116781 - 2³ = 21116773 is a prime.

It is a super-2 number, since 2×21116781² = 891836879603922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21116701) 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 19 ways as a sum of consecutive naturals, for example, 18055 + ... + 19188.

Almost surely, 2^21116781 is an apocalyptic number.

21116781 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21116781 is a deficient number, since it is larger than the sum of its proper divisors (14935411).

21116781 is an equidigital number, since it uses as much as digits as its factorization.

21116781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37262 (or 37253 counting only the distinct ones).

The product of its digits is 672, while the sum is 27.

The square root of 21116781 is about 4595.2998814006. The cubic root of 21116781 is about 276.4028851458.

Adding to 21116781 its reverse (18761112), we get a palindrome (39877893).

The spelling of 21116781 in words is "twenty-one million, one hundred sixteen thousand, seven hundred eighty-one".