1001981 has 2 divisors, whose sum is σ = 1001982. Its totient is φ = 1001980.

The previous prime is 1001977. The next prime is 1001983. The reversal of 1001981 is 1891001.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 931225 + 70756 = 965^2 + 266^2 .

It is a cyclic number.

It is not a de Polignac number, because 1001981 - 2² = 1001977 is a prime.

It is a super-2 number, since 2×1001981² = 2007931848722, which contains 22 as substring.

Together with 1001983, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1001983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 500990 + 500991.

It is an arithmetic number, because the mean of its divisors is an integer number (500991).

2^1001981 is an apocalyptic number.

It is an amenable number.

1001981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1001981 is an equidigital number, since it uses as much as digits as its factorization.

1001981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72, while the sum is 20.

The square root of 1001981 is about 1000.9900099402. The cubic root of 1001981 is about 100.0659897772.

Adding to 1001981 its sum of digits (20), we get a palindrome (1002001).

Adding to 1001981 its reverse (1891001), we get a palindrome (2892982).

The spelling of 1001981 in words is "one million, one thousand, nine hundred eighty-one".