18656437981 has 2 divisors, whose sum is σ = 18656437982. Its totient is φ = 18656437980.

The previous prime is 18656437979. The next prime is 18656438039. The reversal of 18656437981 is 18973465681.

It is an a-pointer prime, because the next prime (18656438039) can be obtained adding 18656437981 to its sum of digits (58).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17197961881 + 1458476100 = 131141^2 + 38190^2 .

It is a cyclic number.

It is not a de Polignac number, because 18656437981 - 2¹ = 18656437979 is a prime.

It is a super-2 number, since 2×18656437981² (a number of 21 digits) contains 22 as substring.

Together with 18656437979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18656437951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9328218990 + 9328218991.

It is an arithmetic number, because the mean of its divisors is an integer number (9328218991).

Almost surely, 2^18656437981 is an apocalyptic number.

It is an amenable number.

18656437981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18656437981 is an equidigital number, since it uses as much as digits as its factorization.

18656437981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8709120, while the sum is 58.

The spelling of 18656437981 in words is "eighteen billion, six hundred fifty-six million, four hundred thirty-seven thousand, nine hundred eighty-one".