21765649 has 4 divisors (see below), whose sum is σ = 21891636. Its totient is φ = 21639664.

The previous prime is 21765647. The next prime is 21765683. The reversal of 21765649 is 94656712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8661249 + 13104400 = 2943^2 + 3620^2 .

It is a cyclic number.

It is not a de Polignac number, because 21765649 - 2¹ = 21765647 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21765643) 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, 62734 + ... + 63079.

It is an arithmetic number, because the mean of its divisors is an integer number (5472909).

Almost surely, 2^21765649 is an apocalyptic number.

It is an amenable number.

21765649 is a deficient number, since it is larger than the sum of its proper divisors (125987).

21765649 is a wasteful number, since it uses less digits than its factorization.

21765649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125986.

The product of its digits is 90720, while the sum is 40.

The square root of 21765649 is about 4665.3669737760. The cubic root of 21765649 is about 279.2054387178.

The spelling of 21765649 in words is "twenty-one million, seven hundred sixty-five thousand, six hundred forty-nine".