20641981 has 2 divisors, whose sum is σ = 20641982. Its totient is φ = 20641980.

The previous prime is 20641969. The next prime is 20641987. The reversal of 20641981 is 18914602.

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., 16402500 + 4239481 = 4050^2 + 2059^2 .

It is a cyclic number.

It is not a de Polignac number, because 20641981 - 2⁷ = 20641853 is a prime.

It is a super-2 number, since 2×20641981² = 852182759208722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20641987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10320990 + 10320991.

It is an arithmetic number, because the mean of its divisors is an integer number (10320991).

Almost surely, 2^20641981 is an apocalyptic number.

It is an amenable number.

20641981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20641981 is an equidigital number, since it uses as much as digits as its factorization.

20641981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 20641981 is about 4543.3446930648. The cubic root of 20641981 is about 274.3155696023.

The spelling of 20641981 in words is "twenty million, six hundred forty-one thousand, nine hundred eighty-one".