681897781 has 4 divisors (see below), whose sum is σ = 683122572. Its totient is φ = 680672992.

The previous prime is 681897739. The next prime is 681897809. The reversal of 681897781 is 187798186.

It is a happy number.

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 337052881 + 344844900 = 18359^2 + 18570^2 .

It is a cyclic number.

It is not a de Polignac number, because 681897781 - 2⁷ = 681897653 is a prime.

It is a super-2 number, since 2×681897781² = 929969167465447922, 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 (681897701) 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, 611560 + ... + 612673.

It is an arithmetic number, because the mean of its divisors is an integer number (170780643).

Almost surely, 2^681897781 is an apocalyptic number.

It is an amenable number.

681897781 is a deficient number, since it is larger than the sum of its proper divisors (1224791).

681897781 is a wasteful number, since it uses less digits than its factorization.

681897781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1224790.

The product of its digits is 1354752, while the sum is 55.

The square root of 681897781 is about 26113.1725571597. The cubic root of 681897781 is about 880.1832353458.

The spelling of 681897781 in words is "six hundred eighty-one million, eight hundred ninety-seven thousand, seven hundred eighty-one".