21751666 has 4 divisors (see below), whose sum is σ = 32627502. Its totient is φ = 10875832.

The previous prime is 21751661. The next prime is 21751669. The reversal of 21751666 is 66615712.

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 only one way, i.e., 19175641 + 2576025 = 4379^2 + 1605^2 .

It is not an unprimeable number, because it can be changed into a prime (21751661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5437915 + ... + 5437918.

Almost surely, 2^21751666 is an apocalyptic number.

21751666 is a deficient number, since it is larger than the sum of its proper divisors (10875836).

21751666 is a wasteful number, since it uses less digits than its factorization.

21751666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10875835.

The product of its digits is 15120, while the sum is 34.

The square root of 21751666 is about 4663.8681370725. The cubic root of 21751666 is about 279.1456355236.

The spelling of 21751666 in words is "twenty-one million, seven hundred fifty-one thousand, six hundred sixty-six".