21653993 has 2 divisors, whose sum is σ = 21653994. Its totient is φ = 21653992.

The previous prime is 21653987. The next prime is 21654001. The reversal of 21653993 is 39935612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14961424 + 6692569 = 3868^2 + 2587^2 .

It is a cyclic number.

It is not a de Polignac number, because 21653993 - 2¹⁸ = 21391849 is a prime.

It is not a weakly prime, because it can be changed into another prime (21653893) 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, 10826996 + 10826997.

It is an arithmetic number, because the mean of its divisors is an integer number (10826997).

Almost surely, 2^21653993 is an apocalyptic number.

It is an amenable number.

21653993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21653993 is an equidigital number, since it uses as much as digits as its factorization.

21653993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 43740, while the sum is 38.

The square root of 21653993 is about 4653.3851119373. The cubic root of 21653993 is about 278.7271862927.

The spelling of 21653993 in words is "twenty-one million, six hundred fifty-three thousand, nine hundred ninety-three".