51492731981 has 4 divisors (see below), whose sum is σ = 51514730364. Its totient is φ = 51470733600.

The previous prime is 51492731977. The next prime is 51492731989. The reversal of 51492731981 is 18913729415.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 33134920900 + 18357811081 = 182030^2 + 135491^2 .

It is a cyclic number.

It is not a de Polignac number, because 51492731981 - 2² = 51492731977 is a prime.

It is a super-2 number, since 2×51492731981² (a number of 22 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51492731989) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10995680 + ... + 11000361.

It is an arithmetic number, because the mean of its divisors is an integer number (12878682591).

Almost surely, 2^51492731981 is an apocalyptic number.

It is an amenable number.

51492731981 is a deficient number, since it is larger than the sum of its proper divisors (21998383).

51492731981 is a wasteful number, since it uses less digits than its factorization.

51492731981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21998382.

The product of its digits is 544320, while the sum is 50.

The spelling of 51492731981 in words is "fifty-one billion, four hundred ninety-two million, seven hundred thirty-one thousand, nine hundred eighty-one".