9919781381 has 2 divisors, whose sum is σ = 9919781382. Its totient is φ = 9919781380.

The previous prime is 9919781351. The next prime is 9919781393. The reversal of 9919781381 is 1831879199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 7667804356 + 2251977025 = 87566^2 + 47455^2 .

It is an emirp because it is prime and its reverse (1831879199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 9919781381 - 2⁶ = 9919781317 is a prime.

It is a super-2 number, since 2×9919781381² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9919781351) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4959890690 + 4959890691.

It is an arithmetic number, because the mean of its divisors is an integer number (4959890691).

Almost surely, 2^9919781381 is an apocalyptic number.

It is an amenable number.

9919781381 is a deficient number, since it is larger than the sum of its proper divisors (1).

9919781381 is an equidigital number, since it uses as much as digits as its factorization.

9919781381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 979776, while the sum is 56.

The square root of 9919781381 is about 99598.0992840727. The cubic root of 9919781381 is about 2148.6583575544.

The spelling of 9919781381 in words is "nine billion, nine hundred nineteen million, seven hundred eighty-one thousand, three hundred eighty-one".