77681921 has 8 divisors (see below), whose sum is σ = 79997064. Its totient is φ = 75386880.

The previous prime is 77681917. The next prime is 77681927. The reversal of 77681921 is 12918677.

It can be written as a sum of positive squares in 4 ways, for example, as 8042896 + 69639025 = 2836^2 + 8345^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 77681921 - 2² = 77681917 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (41).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (77681927) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3005 + ... + 12821.

It is an arithmetic number, because the mean of its divisors is an integer number (9999633).

Almost surely, 2^77681921 is an apocalyptic number.

It is an amenable number.

77681921 is a deficient number, since it is larger than the sum of its proper divisors (2315143).

77681921 is a wasteful number, since it uses less digits than its factorization.

77681921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10051.

The product of its digits is 42336, while the sum is 41.

The square root of 77681921 is about 8813.7347929241. The cubic root of 77681921 is about 426.6842892976.

Subtracting from 77681921 its sum of digits (41), we obtain a triangular number (77681880 = T₁₂₄₆₄).

The spelling of 77681921 in words is "seventy-seven million, six hundred eighty-one thousand, nine hundred twenty-one".