21861840 has 360 divisors, whose sum is σ = 93127968. Its totient is φ = 4193280.

The previous prime is 21861839. The next prime is 21861859. The reversal of 21861840 is 4816812.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21861798 and 21861807.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 1681674 + ... + 1681686.

Almost surely, 2^21861840 is an apocalyptic number.

21861840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21861840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (46563984).

21861840 is an abundant number, since it is smaller than the sum of its proper divisors (71266128).

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

21861840 is a wasteful number, since it uses less digits than its factorization.

21861840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67 (or 41 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 30.

The square root of 21861840 is about 4675.6646586341. The cubic root of 21861840 is about 279.6161406643.

The spelling of 21861840 in words is "twenty-one million, eight hundred sixty-one thousand, eight hundred forty".