21569749 has 2 divisors, whose sum is σ = 21569750. Its totient is φ = 21569748.

The previous prime is 21569689. The next prime is 21569771. The reversal of 21569749 is 94796512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16080100 + 5489649 = 4010^2 + 2343^2 .

It is a cyclic number.

It is not a de Polignac number, because 21569749 - 2⁷ = 21569621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21369749) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10784874 + 10784875.

It is an arithmetic number, because the mean of its divisors is an integer number (10784875).

Almost surely, 2^21569749 is an apocalyptic number.

It is an amenable number.

21569749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21569749 is an equidigital number, since it uses as much as digits as its factorization.

21569749 is an evil number, because the sum of its binary digits is even.

The product of its digits is 136080, while the sum is 43.

The square root of 21569749 is about 4644.3243857422. The cubic root of 21569749 is about 278.3652575125.

The spelling of 21569749 in words is "twenty-one million, five hundred sixty-nine thousand, seven hundred forty-nine".