20649721 has 2 divisors, whose sum is σ = 20649722. Its totient is φ = 20649720.

The previous prime is 20649709. The next prime is 20649743. The reversal of 20649721 is 12794602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17943696 + 2706025 = 4236^2 + 1645^2 .

It is a cyclic number.

It is not a de Polignac number, because 20649721 - 2⁷ = 20649593 is a prime.

It is not a weakly prime, because it can be changed into another prime (20649821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10324860 + 10324861.

It is an arithmetic number, because the mean of its divisors is an integer number (10324861).

Almost surely, 2^20649721 is an apocalyptic number.

It is an amenable number.

20649721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20649721 is an equidigital number, since it uses as much as digits as its factorization.

20649721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6048, while the sum is 31.

The square root of 20649721 is about 4544.1964086074. The cubic root of 20649721 is about 274.3498514733.

The spelling of 20649721 in words is "twenty million, six hundred forty-nine thousand, seven hundred twenty-one".