11531999981 has 2 divisors, whose sum is σ = 11531999982. Its totient is φ = 11531999980.

The previous prime is 11531999939. The next prime is 11532000037. The reversal of 11531999981 is 18999913511.

It is an a-pointer prime, because the next prime (11532000037) can be obtained adding 11531999981 to its sum of digits (56).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8354874025 + 3177125956 = 91405^2 + 56366^2 .

It is an emirp because it is prime and its reverse (18999913511) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 11531999981 - 2¹⁴ = 11531983597 is a prime.

It is a super-2 number, since 2×11531999981² (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 (11531999911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5765999990 + 5765999991.

It is an arithmetic number, because the mean of its divisors is an integer number (5765999991).

Almost surely, 2^11531999981 is an apocalyptic number.

It is an amenable number.

11531999981 is a deficient number, since it is larger than the sum of its proper divisors (1).

11531999981 is an equidigital number, since it uses as much as digits as its factorization.

11531999981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 787320, while the sum is 56.

The spelling of 11531999981 in words is "eleven billion, five hundred thirty-one million, nine hundred ninety-nine thousand, nine hundred eighty-one".