20721637 has 2 divisors, whose sum is σ = 20721638. Its totient is φ = 20721636.

The previous prime is 20721629. The next prime is 20721683. The reversal of 20721637 is 73612702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17313921 + 3407716 = 4161^2 + 1846^2 .

It is a cyclic number.

It is not a de Polignac number, because 20721637 - 2³ = 20721629 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20721037) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360818 + 10360819.

It is an arithmetic number, because the mean of its divisors is an integer number (10360819).

Almost surely, 2^20721637 is an apocalyptic number.

It is an amenable number.

20721637 is a deficient number, since it is larger than the sum of its proper divisors (1).

20721637 is an equidigital number, since it uses as much as digits as its factorization.

20721637 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3528, while the sum is 28.

The square root of 20721637 is about 4552.1024812717. The cubic root of 20721637 is about 274.6679717303.

The spelling of 20721637 in words is "twenty million, seven hundred twenty-one thousand, six hundred thirty-seven".