21117870 has 96 divisors (see below), whose sum is σ = 57788640. Its totient is φ = 5345280.

The previous prime is 21117869. The next prime is 21117871. The reversal of 21117870 is 7871112.

It is an interprime number because it is at equal distance from previous prime (21117869) and next prime (21117871).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21117871) 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 in 47 ways as a sum of consecutive naturals, for example, 217662 + ... + 217758.

It is an arithmetic number, because the mean of its divisors is an integer number (601965).

Almost surely, 2^21117870 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21117870, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28894320).

21117870 is an abundant number, since it is smaller than the sum of its proper divisors (36670770).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21117870 is a wasteful number, since it uses less digits than its factorization.

21117870 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 210 (or 207 counting only the distinct ones).

The product of its (nonzero) digits is 784, while the sum is 27.

The square root of 21117870 is about 4595.4183705077. The cubic root of 21117870 is about 276.4076364629.

Adding to 21117870 its reverse (7871112), we get a palindrome (28988982).

It can be divided in two parts, 211 and 17870, that added together give a palindrome (18081).

The spelling of 21117870 in words is "twenty-one million, one hundred seventeen thousand, eight hundred seventy".