21248781 has 4 divisors (see below), whose sum is σ = 28331712. Its totient is φ = 14165852.

The previous prime is 21248779. The next prime is 21248807. The reversal of 21248781 is 18784212.

It is a happy number.

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 21248781 - 2¹ = 21248779 is a prime.

It is a super-2 number, since 2×21248781² = 903021387971922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21248771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3541461 + ... + 3541466.

It is an arithmetic number, because the mean of its divisors is an integer number (7082928).

Almost surely, 2^21248781 is an apocalyptic number.

It is an amenable number.

21248781 is a deficient number, since it is larger than the sum of its proper divisors (7082931).

21248781 is an equidigital number, since it uses as much as digits as its factorization.

21248781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7082930.

The product of its digits is 7168, while the sum is 33.

The square root of 21248781 is about 4609.6400076362. The cubic root of 21248781 is about 276.9776163887.

The spelling of 21248781 in words is "twenty-one million, two hundred forty-eight thousand, seven hundred eighty-one".