2561981 has 2 divisors, whose sum is σ = 2561982. Its totient is φ = 2561980.

The previous prime is 2561969. The next prime is 2561987. The reversal of 2561981 is 1891652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 2544025 + 17956 = 1595^2 + 134^2 .

It is a cyclic number.

It is not a de Polignac number, because 2561981 - 2¹⁸ = 2299837 is a prime.

It is a super-2 number, since 2×2561981² = 13127493288722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2561987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1280990 + 1280991.

It is an arithmetic number, because the mean of its divisors is an integer number (1280991).

2^2561981 is an apocalyptic number.

It is an amenable number.

2561981 is a deficient number, since it is larger than the sum of its proper divisors (1).

2561981 is an equidigital number, since it uses as much as digits as its factorization.

2561981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 32.

The square root of 2561981 is about 1600.6189427843. The cubic root of 2561981 is about 136.8333527024.

The spelling of 2561981 in words is "two million, five hundred sixty-one thousand, nine hundred eighty-one".