21206993 has 2 divisors, whose sum is σ = 21206994. Its totient is φ = 21206992.

The previous prime is 21206987. The next prime is 21207037. The reversal of 21206993 is 39960212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20948929 + 258064 = 4577^2 + 508^2 .

It is a cyclic number.

It is not a de Polignac number, because 21206993 - 2²² = 17012689 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21206923) 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, 10603496 + 10603497.

It is an arithmetic number, because the mean of its divisors is an integer number (10603497).

Almost surely, 2^21206993 is an apocalyptic number.

It is an amenable number.

21206993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21206993 is an equidigital number, since it uses as much as digits as its factorization.

21206993 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5832, while the sum is 32.

The square root of 21206993 is about 4605.1051019494. The cubic root of 21206993 is about 276.7959285336.

The spelling of 21206993 in words is "twenty-one million, two hundred six thousand, nine hundred ninety-three".