1986805981 has 2 divisors, whose sum is σ = 1986805982. Its totient is φ = 1986805980.

The previous prime is 1986805967. The next prime is 1986805991. The reversal of 1986805981 is 1895086891.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1974380356 + 12425625 = 44434^2 + 3525^2 .

It is an emirp because it is prime and its reverse (1895086891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1986805981 - 2¹¹ = 1986803933 is a prime.

It is a super-2 number, since 2×1986805981² = 7894796012274744722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1986805901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 993402990 + 993402991.

It is an arithmetic number, because the mean of its divisors is an integer number (993402991).

Almost surely, 2^1986805981 is an apocalyptic number.

It is an amenable number.

1986805981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1986805981 is an equidigital number, since it uses as much as digits as its factorization.

1986805981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1244160, while the sum is 55.

The square root of 1986805981 is about 44573.6018401026. The cubic root of 1986805981 is about 1257.1443645957.

The spelling of 1986805981 in words is "one billion, nine hundred eighty-six million, eight hundred five thousand, nine hundred eighty-one".