72111781 has 6 divisors (see below), whose sum is σ = 83885190. Its totient is φ = 61810056.

The previous prime is 72111751. The next prime is 72111799. The reversal of 72111781 is 18711127.

It can be written as a sum of positive squares in only one way, i.e., 71740900 + 370881 = 8470^2 + 609^2 .

It is not a de Polignac number, because 72111781 - 2⁹ = 72111269 is a prime.

It is a super-2 number, since 2×72111781² = 10400217917983922, which 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 (72111751) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 735786 + ... + 735883.

It is an arithmetic number, because the mean of its divisors is an integer number (13980865).

Almost surely, 2^72111781 is an apocalyptic number.

It is an amenable number.

72111781 is a deficient number, since it is larger than the sum of its proper divisors (11773409).

72111781 is a wasteful number, since it uses less digits than its factorization.

72111781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1471683 (or 1471676 counting only the distinct ones).

The product of its digits is 784, while the sum is 28.

The square root of 72111781 is about 8491.8655783049. The cubic root of 72111781 is about 416.2319438942.

The spelling of 72111781 in words is "seventy-two million, one hundred eleven thousand, seven hundred eighty-one".