21982781 has 2 divisors, whose sum is σ = 21982782. Its totient is φ = 21982780.

The previous prime is 21982769. The next prime is 21982787. The reversal of 21982781 is 18728912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18619225 + 3363556 = 4315^2 + 1834^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21982781 is a prime.

It is a super-2 number, since 2×21982781² = 966485320987922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21982787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10991390 + 10991391.

It is an arithmetic number, because the mean of its divisors is an integer number (10991391).

Almost surely, 2^21982781 is an apocalyptic number.

It is an amenable number.

21982781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21982781 is an equidigital number, since it uses as much as digits as its factorization.

21982781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16128, while the sum is 38.

The square root of 21982781 is about 4688.5798489521. The cubic root of 21982781 is about 280.1308104770.

The spelling of 21982781 in words is "twenty-one million, nine hundred eighty-two thousand, seven hundred eighty-one".