21017993 has 2 divisors, whose sum is σ = 21017994. Its totient is φ = 21017992.

The previous prime is 21017981. The next prime is 21018043. The reversal of 21017993 is 39971012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17909824 + 3108169 = 4232^2 + 1763^2 .

It is a cyclic number.

It is not a de Polignac number, because 21017993 - 2¹⁶ = 20952457 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21017093) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10508996 + 10508997.

It is an arithmetic number, because the mean of its divisors is an integer number (10508997).

Almost surely, 2^21017993 is an apocalyptic number.

It is an amenable number.

21017993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21017993 is an equidigital number, since it uses as much as digits as its factorization.

21017993 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3402, while the sum is 32.

The square root of 21017993 is about 4584.5384718639. The cubic root of 21017993 is about 275.9711908948.

The spelling of 21017993 in words is "twenty-one million, seventeen thousand, nine hundred ninety-three".