21970981 has 2 divisors, whose sum is σ = 21970982. Its totient is φ = 21970980.

The previous prime is 21970969. The next prime is 21971017. The reversal of 21970981 is 18907912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21473956 + 497025 = 4634^2 + 705^2 .

It is a cyclic number.

It is not a de Polignac number, because 21970981 - 2⁹ = 21970469 is a prime.

It is a super-2 number, since 2×21970981² = 965448012204722, which contains 22 as substring.

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 21970981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21970901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10985490 + 10985491.

It is an arithmetic number, because the mean of its divisors is an integer number (10985491).

Almost surely, 2^21970981 is an apocalyptic number.

It is an amenable number.

21970981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21970981 is an equidigital number, since it uses as much as digits as its factorization.

21970981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21970981 is about 4687.3213032605. The cubic root of 21970981 is about 280.0806782820.

The spelling of 21970981 in words is "twenty-one million, nine hundred seventy thousand, nine hundred eighty-one".