921681 has 6 divisors (see below), whose sum is σ = 1331330. Its totient is φ = 614448.

The previous prime is 921677. The next prime is 921703. The reversal of 921681 is 186129.

It can be written as a sum of positive squares in only one way, i.e., 921600 + 81 = 960^2 + 9^2 .

It is not a de Polignac number, because 921681 - 2² = 921677 is a prime.

It is a super-2 number, since 2×921681² = 1698991731522, which contains 22 as substring.

It is a Duffinian number.

921681 is a lucky number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 921681.

It is not an unprimeable number, because it can be changed into a prime (921601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 51196 + ... + 51213.

2⁹²¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

921681 is a deficient number, since it is larger than the sum of its proper divisors (409649).

921681 is a wasteful number, since it uses less digits than its factorization.

921681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 102415 (or 102412 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 921681 is about 960.0421865731. The cubic root of 921681 is about 97.3180828778.

It can be divided in two parts, 9216 and 81, that multiplied together give a square (746496 = 864²).

The spelling of 921681 in words is "nine hundred twenty-one thousand, six hundred eighty-one".