21686690 has 8 divisors (see below), whose sum is σ = 39036060. Its totient is φ = 8674672.

The previous prime is 21686671. The next prime is 21686741. The reversal of 21686690 is 9668612.

It can be written as a sum of positive squares in 2 ways, for example, as 18550249 + 3136441 = 4307^2 + 1771^2 .

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

It is a super-2 number, since 2×21686690² = 940625046312200, 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 3 ways as a sum of consecutive naturals, for example, 1084325 + ... + 1084344.

Almost surely, 2^21686690 is an apocalyptic number.

21686690 is a deficient number, since it is larger than the sum of its proper divisors (17349370).

21686690 is a wasteful number, since it uses less digits than its factorization.

21686690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2168676.

The product of its (nonzero) digits is 31104, while the sum is 38.

The square root of 21686690 is about 4656.8970355807. The cubic root of 21686690 is about 278.8674061524.

The spelling of 21686690 in words is "twenty-one million, six hundred eighty-six thousand, six hundred ninety".