21243690 has 96 divisors (see below), whose sum is σ = 60592896. Its totient is φ = 5132160.

The previous prime is 21243683. The next prime is 21243707. The reversal of 21243690 is 9634212.

It is a super-2 number, since 2×21243690² = 902588729632200, which contains 22 as substring.

It is an unprimeable number.

It is a nontrivial repunit in base 29.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 78255 + ... + 78525.

It is an arithmetic number, because the mean of its divisors is an integer number (631176).

Almost surely, 2^21243690 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21243690, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30296448).

21243690 is an abundant number, since it is smaller than the sum of its proper divisors (39349206).

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

21243690 is a wasteful number, since it uses less digits than its factorization.

21243690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 364 (or 361 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 27.

The square root of 21243690 is about 4609.0877622367. The cubic root of 21243690 is about 276.9554942463.

The spelling of 21243690 in words is "twenty-one million, two hundred forty-three thousand, six hundred ninety".