13615821981 has 16 divisors (see below), whose sum is σ = 20198766720. Its totient is φ = 9064984320.

The previous prime is 13615821949. The next prime is 13615821991. The reversal of 13615821981 is 18912851631.

13615821981 is a `hidden beast` number, since 1 + 3 + 61 + 582 + 1 + 9 + 8 + 1 = 666.

It is not a de Polignac number, because 13615821981 - 2⁵ = 13615821949 is a prime.

It is a super-2 number, since 2×13615821981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (13615821991) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 319300 + ... + 359421.

It is an arithmetic number, because the mean of its divisors is an integer number (1262422920).

Almost surely, 2^13615821981 is an apocalyptic number.

It is an amenable number.

13615821981 is a deficient number, since it is larger than the sum of its proper divisors (6582944739).

13615821981 is an equidigital number, since it uses as much as digits as its factorization.

13615821981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 679473 (or 679467 counting only the distinct ones).

The product of its digits is 103680, while the sum is 45.

The spelling of 13615821981 in words is "thirteen billion, six hundred fifteen million, eight hundred twenty-one thousand, nine hundred eighty-one".