189781981 has 2 divisors, whose sum is σ = 189781982. Its totient is φ = 189781980.

The previous prime is 189781967. The next prime is 189781997. The reversal of 189781981 is 189187981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 115218756 + 74563225 = 10734^2 + 8635^2 .

It is a cyclic number.

It is not a de Polignac number, because 189781981 - 2⁹ = 189781469 is a prime.

It is a super-2 number, since 2×189781981² = 72034400624568722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (189781381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 94890990 + 94890991.

It is an arithmetic number, because the mean of its divisors is an integer number (94890991).

Almost surely, 2^189781981 is an apocalyptic number.

It is an amenable number.

189781981 is a deficient number, since it is larger than the sum of its proper divisors (1).

189781981 is an equidigital number, since it uses as much as digits as its factorization.

189781981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 290304, while the sum is 52.

The square root of 189781981 is about 13776.1381018049. The cubic root of 189781981 is about 574.6697344737.

The spelling of 189781981 in words is "one hundred eighty-nine million, seven hundred eighty-one thousand, nine hundred eighty-one".