21088781 has 4 divisors (see below), whose sum is σ = 24101472. Its totient is φ = 18076092.

The previous prime is 21088763. The next prime is 21088787. The reversal of 21088781 is 18788012.

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 a de Polignac number, because none of the positive numbers 2^k-21088781 is a prime.

It is a super-2 number, since 2×21088781² = 889473368131922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21088787) 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, 1506335 + ... + 1506348.

It is an arithmetic number, because the mean of its divisors is an integer number (6025368).

Almost surely, 2^21088781 is an apocalyptic number.

It is an amenable number.

21088781 is a deficient number, since it is larger than the sum of its proper divisors (3012691).

21088781 is an equidigital number, since it uses as much as digits as its factorization.

21088781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3012690.

The product of its (nonzero) digits is 7168, while the sum is 35.

The square root of 21088781 is about 4592.2522796554. The cubic root of 21088781 is about 276.2806647505.

The spelling of 21088781 in words is "twenty-one million, eighty-eight thousand, seven hundred eighty-one".