21988957 has 2 divisors, whose sum is σ = 21988958. Its totient is φ = 21988956.

The previous prime is 21988937. The next prime is 21988969. The reversal of 21988957 is 75988912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20196036 + 1792921 = 4494^2 + 1339^2 .

It is a cyclic number.

It is not a de Polignac number, because 21988957 - 2⁷ = 21988829 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21988957.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21988937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10994478 + 10994479.

It is an arithmetic number, because the mean of its divisors is an integer number (10994479).

Almost surely, 2^21988957 is an apocalyptic number.

It is an amenable number.

21988957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21988957 is an equidigital number, since it uses as much as digits as its factorization.

21988957 is an evil number, because the sum of its binary digits is even.

The product of its digits is 362880, while the sum is 49.

The square root of 21988957 is about 4689.2384243073. The cubic root of 21988957 is about 280.1570420063.

The spelling of 21988957 in words is "twenty-one million, nine hundred eighty-eight thousand, nine hundred fifty-seven".