21947861 has 12 divisors (see below), whose sum is σ = 24166980. Its totient is φ = 19918080.

The previous prime is 21947857. The next prime is 21947897. The reversal of 21947861 is 16874912.

It can be written as a sum of positive squares in 6 ways, for example, as 11771761 + 10176100 = 3431^2 + 3190^2 .

It is not a de Polignac number, because 21947861 - 2² = 21947857 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21947801) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9245 + ... + 11373.

It is an arithmetic number, because the mean of its divisors is an integer number (2013915).

Almost surely, 2^21947861 is an apocalyptic number.

It is an amenable number.

21947861 is a deficient number, since it is larger than the sum of its proper divisors (2219119).

21947861 is a wasteful number, since it uses less digits than its factorization.

21947861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2216 (or 2203 counting only the distinct ones).

The product of its digits is 24192, while the sum is 38.

The square root of 21947861 is about 4684.8544267672. The cubic root of 21947861 is about 279.9824011048.

The spelling of 21947861 in words is "twenty-one million, nine hundred forty-seven thousand, eight hundred sixty-one".