21749447 has 2 divisors, whose sum is σ = 21749448. Its totient is φ = 21749446.

The previous prime is 21749423. The next prime is 21749459. The reversal of 21749447 is 74494712.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21749447 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21749447.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21742447) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10874723 + 10874724.

It is an arithmetic number, because the mean of its divisors is an integer number (10874724).

Almost surely, 2^21749447 is an apocalyptic number.

21749447 is a deficient number, since it is larger than the sum of its proper divisors (1).

21749447 is an equidigital number, since it uses as much as digits as its factorization.

21749447 is an evil number, because the sum of its binary digits is even.

The product of its digits is 56448, while the sum is 38.

The square root of 21749447 is about 4663.6302383444. The cubic root of 21749447 is about 279.1361428373.

The spelling of 21749447 in words is "twenty-one million, seven hundred forty-nine thousand, four hundred forty-seven".