9901981 has 2 divisors, whose sum is σ = 9901982. Its totient is φ = 9901980.

The previous prime is 9901901. The next prime is 9901987. The reversal of 9901981 is 1891099.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 9865881 + 36100 = 3141^2 + 190^2 .

It is a cyclic number.

It is not a de Polignac number, because 9901981 - 2¹³ = 9893789 is a prime.

It is a super-2 number, since 2×9901981² = 196098455448722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 9901981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9901987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4950990 + 4950991.

It is an arithmetic number, because the mean of its divisors is an integer number (4950991).

Almost surely, 2^9901981 is an apocalyptic number.

It is an amenable number.

9901981 is a deficient number, since it is larger than the sum of its proper divisors (1).

9901981 is an equidigital number, since it uses as much as digits as its factorization.

9901981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5832, while the sum is 37.

The square root of 9901981 is about 3146.7413303289. The cubic root of 9901981 is about 214.7372380376.

It can be divided in two parts, 990 and 1981, that multiplied together give a triangular number (1961190 = T₁₉₈₀).

The spelling of 9901981 in words is "nine million, nine hundred one thousand, nine hundred eighty-one".