20617981 has 2 divisors, whose sum is σ = 20617982. Its totient is φ = 20617980.

The previous prime is 20617943. The next prime is 20617999. The reversal of 20617981 is 18971602.

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., 20169081 + 448900 = 4491^2 + 670^2 .

It is a cyclic number.

It is not a de Polignac number, because 20617981 - 2⁹ = 20617469 is a prime.

It is a super-2 number, since 2×20617981² = 850202281032722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20617921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10308990 + 10308991.

It is an arithmetic number, because the mean of its divisors is an integer number (10308991).

Almost surely, 2^20617981 is an apocalyptic number.

It is an amenable number.

20617981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20617981 is an equidigital number, since it uses as much as digits as its factorization.

20617981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 20617981 is about 4540.7026989223. The cubic root of 20617981 is about 274.2092147124.

The spelling of 20617981 in words is "twenty million, six hundred seventeen thousand, nine hundred eighty-one".