20899721 has 2 divisors, whose sum is σ = 20899722. Its totient is φ = 20899720.

The previous prime is 20899699. The next prime is 20899733. The reversal of 20899721 is 12799802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11833600 + 9066121 = 3440^2 + 3011^2 .

It is a cyclic number.

It is not a de Polignac number, because 20899721 - 2¹⁸ = 20637577 is a prime.

It is not a weakly prime, because it can be changed into another prime (20899751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10449860 + 10449861.

It is an arithmetic number, because the mean of its divisors is an integer number (10449861).

Almost surely, 2^20899721 is an apocalyptic number.

It is an amenable number.

20899721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20899721 is an equidigital number, since it uses as much as digits as its factorization.

20899721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 20899721 is about 4571.6212660281. The cubic root of 20899721 is about 275.4525704937.

The spelling of 20899721 in words is "twenty million, eight hundred ninety-nine thousand, seven hundred twenty-one".