21006751 has 4 divisors (see below), whose sum is σ = 21920112. Its totient is φ = 20093392.

The previous prime is 21006743. The next prime is 21006779. The reversal of 21006751 is 15760012.

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

It is a cyclic number.

It is not a de Polignac number, because 21006751 - 2³ = 21006743 is a prime.

It is a super-3 number, since 3×21006751³ (a number of 23 digits) contains 333 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 (21006731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 456646 + ... + 456691.

It is an arithmetic number, because the mean of its divisors is an integer number (5480028).

Almost surely, 2^21006751 is an apocalyptic number.

21006751 is a deficient number, since it is larger than the sum of its proper divisors (913361).

21006751 is an equidigital number, since it uses as much as digits as its factorization.

21006751 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 913360.

The product of its (nonzero) digits is 420, while the sum is 22.

The square root of 21006751 is about 4583.3122302544. The cubic root of 21006751 is about 275.9219787517.

Adding to 21006751 its reverse (15760012), we get a palindrome (36766763).

The spelling of 21006751 in words is "twenty-one million, six thousand, seven hundred fifty-one".