21317870 has 16 divisors (see below), whose sum is σ = 43854048. Its totient is φ = 7308960.

The previous prime is 21317861. The next prime is 21317873. The reversal of 21317870 is 7871312.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21317873) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 152201 + ... + 152340.

It is an arithmetic number, because the mean of its divisors is an integer number (2740878).

Almost surely, 2^21317870 is an apocalyptic number.

21317870 is an abundant number, since it is smaller than the sum of its proper divisors (22536178).

21317870 is a wasteful number, since it uses less digits than its factorization.

21317870 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 304555.

The product of its (nonzero) digits is 2352, while the sum is 29.

The square root of 21317870 is about 4617.1278951313. The cubic root of 21317870 is about 277.2774830649.

It can be divided in two parts, 2131 and 7870, that added together give a palindrome (10001).

The spelling of 21317870 in words is "twenty-one million, three hundred seventeen thousand, eight hundred seventy".