21156749 has 2 divisors, whose sum is σ = 21156750. Its totient is φ = 21156748.

The previous prime is 21156743. The next prime is 21156763. The reversal of 21156749 is 94765112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11854249 + 9302500 = 3443^2 + 3050^2 .

It is a cyclic number.

It is not a de Polignac number, because 21156749 - 2⁸ = 21156493 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21156743) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578374 + 10578375.

It is an arithmetic number, because the mean of its divisors is an integer number (10578375).

Almost surely, 2^21156749 is an apocalyptic number.

It is an amenable number.

21156749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21156749 is an equidigital number, since it uses as much as digits as its factorization.

21156749 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 35.

The square root of 21156749 is about 4599.6466168609. The cubic root of 21156749 is about 276.5771589940.

The spelling of 21156749 in words is "twenty-one million, one hundred fifty-six thousand, seven hundred forty-nine".