20721737 has 2 divisors, whose sum is σ = 20721738. Its totient is φ = 20721736.

The previous prime is 20721721. The next prime is 20721749. The reversal of 20721737 is 73712702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19882681 + 839056 = 4459^2 + 916^2 .

It is a cyclic number.

It is not a de Polignac number, because 20721737 - 2⁴ = 20721721 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20721787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360868 + 10360869.

It is an arithmetic number, because the mean of its divisors is an integer number (10360869).

Almost surely, 2^20721737 is an apocalyptic number.

It is an amenable number.

20721737 is a deficient number, since it is larger than the sum of its proper divisors (1).

20721737 is an equidigital number, since it uses as much as digits as its factorization.

20721737 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4116, while the sum is 29.

The square root of 20721737 is about 4552.1134651939. The cubic root of 20721737 is about 274.6684135672.

The spelling of 20721737 in words is "twenty million, seven hundred twenty-one thousand, seven hundred thirty-seven".