21017890 has 8 divisors (see below), whose sum is σ = 37832220. Its totient is φ = 8407152.

The previous prime is 21017881. The next prime is 21017897. The reversal of 21017890 is 9871012.

It can be written as a sum of positive squares in 2 ways, for example, as 20875761 + 142129 = 4569^2 + 377^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21017897) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1050885 + ... + 1050904.

Almost surely, 2^21017890 is an apocalyptic number.

21017890 is a deficient number, since it is larger than the sum of its proper divisors (16814330).

21017890 is a wasteful number, since it uses less digits than its factorization.

21017890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2101796.

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 21017890 is about 4584.5272384402. The cubic root of 21017890 is about 275.9707400894.

The spelling of 21017890 in words is "twenty-one million, seventeen thousand, eight hundred ninety".