21082981 has 2 divisors, whose sum is σ = 21082982. Its totient is φ = 21082980.

The previous prime is 21082961. The next prime is 21083017. The reversal of 21082981 is 18928012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13432225 + 7650756 = 3665^2 + 2766^2 .

It is a cyclic number.

It is not a de Polignac number, because 21082981 - 2⁵ = 21082949 is a prime.

It is a super-2 number, since 2×21082981² = 888984175692722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21082961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10541490 + 10541491.

It is an arithmetic number, because the mean of its divisors is an integer number (10541491).

Almost surely, 2^21082981 is an apocalyptic number.

It is an amenable number.

21082981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21082981 is an equidigital number, since it uses as much as digits as its factorization.

21082981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 21082981 is about 4591.6207378223. The cubic root of 21082981 is about 276.2553341449.

The spelling of 21082981 in words is "twenty-one million, eighty-two thousand, nine hundred eighty-one".