21651930 has 48 divisors (see below), whose sum is σ = 56819880. Its totient is φ = 5720064.

The previous prime is 21651907. The next prime is 21651943. The reversal of 21651930 is 3915612.

21651930 is a `hidden beast` number, since 2 + 1 + 651 + 9 + 3 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 7969329 + 13682601 = 2823^2 + 3699^2 .

It is a super-3 number, since 3×21651930³ (a number of 23 digits) contains 333 as substring.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21651894 and 21651903.

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, 9106 + ... + 11234.

Almost surely, 2^21651930 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21651930, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28409940).

21651930 is an abundant number, since it is smaller than the sum of its proper divisors (35167950).

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

21651930 is a wasteful number, since it uses less digits than its factorization.

21651930 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2255 (or 2252 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 21651930 is about 4653.1634400696. The cubic root of 21651930 is about 278.7183344619.

It can be divided in two parts, 2165 and 1930, that added together give a triangular number (4095 = T₉₀).

The spelling of 21651930 in words is "twenty-one million, six hundred fifty-one thousand, nine hundred thirty".