21157749 has 6 divisors (see below), whose sum is σ = 30561206. Its totient is φ = 14105160.

The previous prime is 21157739. The next prime is 21157751. The reversal of 21157749 is 94775112.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 13373649 + 7784100 = 3657^2 + 2790^2 .

It is not a de Polignac number, because 21157749 - 2¹² = 21153653 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21157739) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1175422 + ... + 1175439.

Almost surely, 2^21157749 is an apocalyptic number.

It is an amenable number.

21157749 is a deficient number, since it is larger than the sum of its proper divisors (9403457).

21157749 is a wasteful number, since it uses less digits than its factorization.

21157749 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2350867 (or 2350864 counting only the distinct ones).

The product of its digits is 17640, while the sum is 36.

The square root of 21157749 is about 4599.7553195795. The cubic root of 21157749 is about 276.5815165129.

The spelling of 21157749 in words is "twenty-one million, one hundred fifty-seven thousand, seven hundred forty-nine".