20131981 has 2 divisors, whose sum is σ = 20131982. Its totient is φ = 20131980.

The previous prime is 20131939. The next prime is 20131987. The reversal of 20131981 is 18913102.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17926756 + 2205225 = 4234^2 + 1485^2 .

It is a cyclic number.

It is not a de Polignac number, because 20131981 - 2¹⁷ = 20000909 is a prime.

It is a super-2 number, since 2×20131981² = 810593317968722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20131987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10065990 + 10065991.

It is an arithmetic number, because the mean of its divisors is an integer number (10065991).

Almost surely, 2^20131981 is an apocalyptic number.

It is an amenable number.

20131981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20131981 is an equidigital number, since it uses as much as digits as its factorization.

20131981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 20131981 is about 4486.8676156089. The cubic root of 20131981 is about 272.0375389727.

It can be divided in two parts, 20131 and 981, that added together give a palindrome (21112).

The spelling of 20131981 in words is "twenty million, one hundred thirty-one thousand, nine hundred eighty-one".