20399221 has 2 divisors, whose sum is σ = 20399222. Its totient is φ = 20399220.

The previous prime is 20399213. The next prime is 20399227. The reversal of 20399221 is 12299302.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20160100 + 239121 = 4490^2 + 489^2 .

It is a cyclic number.

It is not a de Polignac number, because 20399221 - 2³ = 20399213 is a prime.

It is a super-2 number, since 2×20399221² = 832256434813682, which contains 22 as substring.

It is equal to p_1294309 and since 20399221 and 1294309 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20399221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20399227) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10199610 + 10199611.

It is an arithmetic number, because the mean of its divisors is an integer number (10199611).

Almost surely, 2^20399221 is an apocalyptic number.

It is an amenable number.

20399221 is a deficient number, since it is larger than the sum of its proper divisors (1).

20399221 is an equidigital number, since it uses as much as digits as its factorization.

20399221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 20399221 is about 4516.5496786817. The cubic root of 20399221 is about 273.2359635664.

The spelling of 20399221 in words is "twenty million, three hundred ninety-nine thousand, two hundred twenty-one".