21981575 has 48 divisors (see below), whose sum is σ = 35831040. Its totient is φ = 12960000.

The previous prime is 21981569. The next prime is 21981577. The reversal of 21981575 is 57518912.

It is not a de Polignac number, because 21981575 - 2⁴ = 21981559 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981577) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 36275 + ... + 36875.

It is an arithmetic number, because the mean of its divisors is an integer number (746480).

Almost surely, 2^21981575 is an apocalyptic number.

21981575 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21981575 is a deficient number, since it is larger than the sum of its proper divisors (13849465).

21981575 is a wasteful number, since it uses less digits than its factorization.

21981575 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 648 (or 643 counting only the distinct ones).

The product of its digits is 25200, while the sum is 38.

The square root of 21981575 is about 4688.4512368158. The cubic root of 21981575 is about 280.1256876200.

It can be divided in two parts, 2198 and 1575, that added together give a palindrome (3773).

The spelling of 21981575 in words is "twenty-one million, nine hundred eighty-one thousand, five hundred seventy-five".