21305737 has 2 divisors, whose sum is σ = 21305738. Its totient is φ = 21305736.

The previous prime is 21305729. The next prime is 21305741. The reversal of 21305737 is 73750312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21013056 + 292681 = 4584^2 + 541^2 .

It is a cyclic number.

It is not a de Polignac number, because 21305737 - 2³ = 21305729 is a prime.

It is a super-2 number, since 2×21305737² = 907868858226338, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21305237) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10652868 + 10652869.

It is an arithmetic number, because the mean of its divisors is an integer number (10652869).

Almost surely, 2^21305737 is an apocalyptic number.

It is an amenable number.

21305737 is a deficient number, since it is larger than the sum of its proper divisors (1).

21305737 is an equidigital number, since it uses as much as digits as its factorization.

21305737 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4410, while the sum is 28.

The square root of 21305737 is about 4615.8137960711. The cubic root of 21305737 is about 277.2248692070.

The spelling of 21305737 in words is "twenty-one million, three hundred five thousand, seven hundred thirty-seven".