21678651 has 8 divisors (see below), whose sum is σ = 32116560. Its totient is φ = 14452416.

The previous prime is 21678623. The next prime is 21678659. The reversal of 21678651 is 15687612.

It is a de Polignac number, because none of the positive numbers 2^k-21678651 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21678659) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 401430 + ... + 401483.

It is an arithmetic number, because the mean of its divisors is an integer number (4014570).

Almost surely, 2^21678651 is an apocalyptic number.

21678651 is a deficient number, since it is larger than the sum of its proper divisors (10437909).

21678651 is an equidigital number, since it uses as much as digits as its factorization.

21678651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 802922 (or 802916 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21678651 is about 4656.0338271967. The cubic root of 21678651 is about 278.8329442752.

The spelling of 21678651 in words is "twenty-one million, six hundred seventy-eight thousand, six hundred fifty-one".