21287690 has 8 divisors (see below), whose sum is σ = 38317860. Its totient is φ = 8515072.

The previous prime is 21287681. The next prime is 21287701. The reversal of 21287690 is 9678212.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 21279769 + 7921 = 4613^2 + 89^2 .

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

It is a super-2 number, since 2×21287690² = 906331491072200, which contains 22 as substring.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21287690.

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, 1064375 + ... + 1064394.

Almost surely, 2^21287690 is an apocalyptic number.

21287690 is a deficient number, since it is larger than the sum of its proper divisors (17030170).

21287690 is a wasteful number, since it uses less digits than its factorization.

21287690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2128776.

The product of its (nonzero) digits is 12096, while the sum is 35.

The square root of 21287690 is about 4613.8584720383. The cubic root of 21287690 is about 277.1465727604.

The spelling of 21287690 in words is "twenty-one million, two hundred eighty-seven thousand, six hundred ninety".