21089781 has 16 divisors (see below), whose sum is σ = 32603520. Its totient is φ = 13448160.

The previous prime is 21089777. The next prime is 21089819. The reversal of 21089781 is 18798012.

It is not a de Polignac number, because 21089781 - 2² = 21089777 is a prime.

It is a super-2 number, since 2×21089781² = 889557725255922, which contains 22 as substring.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21089711) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16360 + ... + 17601.

It is an arithmetic number, because the mean of its divisors is an integer number (2037720).

Almost surely, 2^21089781 is an apocalyptic number.

It is an amenable number.

21089781 is a deficient number, since it is larger than the sum of its proper divisors (11513739).

21089781 is a wasteful number, since it uses less digits than its factorization.

21089781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33993 (or 33987 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 21089781 is about 4592.3611574004. The cubic root of 21089781 is about 276.2850316268.

The spelling of 21089781 in words is "twenty-one million, eighty-nine thousand, seven hundred eighty-one".