21678390 has 48 divisors (see below), whose sum is σ = 57096000. Its totient is φ = 5705856.

The previous prime is 21678389. The next prime is 21678401. The reversal of 21678390 is 9387612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5586 + ... + 8634.

It is an arithmetic number, because the mean of its divisors is an integer number (1189500).

Almost surely, 2^21678390 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21678390, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28548000).

21678390 is an abundant number, since it is smaller than the sum of its proper divisors (35417610).

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

21678390 is a wasteful number, since it uses less digits than its factorization.

21678390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3141 (or 3138 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 21678390 is about 4656.0057989655. The cubic root of 21678390 is about 278.8318252682.

It can be divided in two parts, 216 and 78390, that added together give a triangular number (78606 = T₃₉₆).

The spelling of 21678390 in words is "twenty-one million, six hundred seventy-eight thousand, three hundred ninety".