21985081 has 2 divisors, whose sum is σ = 21985082. Its totient is φ = 21985080.

The previous prime is 21985069. The next prime is 21985091. The reversal of 21985081 is 18058912.

21985081 = 3315² + 3316².

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10995856 + 10989225 = 3316^2 + 3315^2 .

It is a cyclic number.

It is not a de Polignac number, because 21985081 - 2¹⁵ = 21952313 is a prime.

It is a super-2 number, since 2×21985081² = 966687573153122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21985031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10992540 + 10992541.

It is an arithmetic number, because the mean of its divisors is an integer number (10992541).

Almost surely, 2^21985081 is an apocalyptic number.

21985081 is the 3316-th centered square number.

It is an amenable number.

21985081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21985081 is an equidigital number, since it uses as much as digits as its factorization.

21985081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5760, while the sum is 34.

The square root of 21985081 is about 4688.8251193663. The cubic root of 21985081 is about 280.1405799173.

The spelling of 21985081 in words is "twenty-one million, nine hundred eighty-five thousand, eighty-one".