21612749 has 2 divisors, whose sum is σ = 21612750. Its totient is φ = 21612748.

The previous prime is 21612707. The next prime is 21612751. The reversal of 21612749 is 94721612.

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., 18550249 + 3062500 = 4307^2 + 1750^2 .

It is a cyclic number.

It is not a de Polignac number, because 21612749 - 2²⁴ = 4835533 is a prime.

It is a super-2 number, since 2×21612749² = 934221838674002, which contains 22 as substring.

Together with 21612751, it forms a pair of twin primes.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21612769) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10806374 + 10806375.

It is an arithmetic number, because the mean of its divisors is an integer number (10806375).

Almost surely, 2^21612749 is an apocalyptic number.

It is an amenable number.

21612749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21612749 is an equidigital number, since it uses as much as digits as its factorization.

21612749 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6048, while the sum is 32.

The square root of 21612749 is about 4648.9513871410. The cubic root of 21612749 is about 278.5501114773.

The spelling of 21612749 in words is "twenty-one million, six hundred twelve thousand, seven hundred forty-nine".