21987946 has 4 divisors (see below), whose sum is σ = 32981922. Its totient is φ = 10993972.

The previous prime is 21987929. The next prime is 21987947. The reversal of 21987946 is 64978912.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 21986721 + 1225 = 4689^2 + 35^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21987896 and 21987905.

It is not an unprimeable number, because it can be changed into a prime (21987947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5496985 + ... + 5496988.

Almost surely, 2^21987946 is an apocalyptic number.

21987946 is a deficient number, since it is larger than the sum of its proper divisors (10993976).

21987946 is a wasteful number, since it uses less digits than its factorization.

21987946 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10993975.

The product of its digits is 217728, while the sum is 46.

The square root of 21987946 is about 4689.1306230473. The cubic root of 21987946 is about 280.1527482888.

It can be divided in two parts, 21987 and 946, that multiplied together give a palindrome (20799702).

The spelling of 21987946 in words is "twenty-one million, nine hundred eighty-seven thousand, nine hundred forty-six".