21688970 has 16 divisors (see below), whose sum is σ = 39138120. Its totient is φ = 8653824.

The previous prime is 21688969. The next prime is 21688981. The reversal of 21688970 is 7988612.

It can be written as a sum of positive squares in 4 ways, for example, as 12694969 + 8994001 = 3563^2 + 2999^2 .

It is a super-2 number, since 2×21688970² = 940822839321800, which contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1826 + ... + 6834.

Almost surely, 2^21688970 is an apocalyptic number.

21688970 is a deficient number, since it is larger than the sum of its proper divisors (17449150).

21688970 is a wasteful number, since it uses less digits than its factorization.

21688970 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5449.

The product of its (nonzero) digits is 48384, while the sum is 41.

The square root of 21688970 is about 4657.1418273443. The cubic root of 21688970 is about 278.8771785889.

The spelling of 21688970 in words is "twenty-one million, six hundred eighty-eight thousand, nine hundred seventy".