21994981 has 2 divisors, whose sum is σ = 21994982. Its totient is φ = 21994980.

The previous prime is 21994897. The next prime is 21994993. The reversal of 21994981 is 18949912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14945956 + 7049025 = 3866^2 + 2655^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21994981 is a prime.

It is a super-2 number, since 2×21994981² = 967558378380722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21994781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10997490 + 10997491.

It is an arithmetic number, because the mean of its divisors is an integer number (10997491).

Almost surely, 2^21994981 is an apocalyptic number.

It is an amenable number.

21994981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21994981 is an equidigital number, since it uses as much as digits as its factorization.

21994981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 46656, while the sum is 43.

The square root of 21994981 is about 4689.8807021075. The cubic root of 21994981 is about 280.1826232095.

The spelling of 21994981 in words is "twenty-one million, nine hundred ninety-four thousand, nine hundred eighty-one".