21006870 has 16 divisors (see below), whose sum is σ = 50416560. Its totient is φ = 5601824.

The previous prime is 21006863. The next prime is 21006877. The reversal of 21006870 is 7860012.

It is an interprime number because it is at equal distance from previous prime (21006863) and next prime (21006877).

It is a self number, because there is not a number n which added to its sum of digits gives 21006870.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006877) 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, 350085 + ... + 350144.

It is an arithmetic number, because the mean of its divisors is an integer number (3151035).

Almost surely, 2^21006870 is an apocalyptic number.

21006870 is an abundant number, since it is smaller than the sum of its proper divisors (29409690).

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

21006870 is a wasteful number, since it uses less digits than its factorization.

21006870 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 700239.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21006870 is about 4583.3252121140. The cubic root of 21006870 is about 275.9224997692.

Adding to 21006870 its reverse (7860012), we get a palindrome (28866882).

The spelling of 21006870 in words is "twenty-one million, six thousand, eight hundred seventy".