21681658 has 4 divisors (see below), whose sum is σ = 32522490. Its totient is φ = 10840828.

The previous prime is 21681643. The next prime is 21681659. The reversal of 21681658 is 85618612.

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

It can be written as a sum of positive squares in only one way, i.e., 17749369 + 3932289 = 4213^2 + 1983^2 .

It is not an unprimeable number, because it can be changed into a prime (21681659) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5420413 + ... + 5420416.

Almost surely, 2^21681658 is an apocalyptic number.

21681658 is a deficient number, since it is larger than the sum of its proper divisors (10840832).

21681658 is a wasteful number, since it uses less digits than its factorization.

21681658 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10840831.

The product of its digits is 23040, while the sum is 37.

The square root of 21681658 is about 4656.3567303204. The cubic root of 21681658 is about 278.8458357893.

The spelling of 21681658 in words is "twenty-one million, six hundred eighty-one thousand, six hundred fifty-eight".