21685751 has 2 divisors, whose sum is σ = 21685752. Its totient is φ = 21685750.

The previous prime is 21685739. The next prime is 21685787. The reversal of 21685751 is 15758612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21685751 - 2⁶ = 21685687 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21685721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10842875 + 10842876.

It is an arithmetic number, because the mean of its divisors is an integer number (10842876).

Almost surely, 2^21685751 is an apocalyptic number.

21685751 is a deficient number, since it is larger than the sum of its proper divisors (1).

21685751 is an equidigital number, since it uses as much as digits as its factorization.

21685751 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16800, while the sum is 35.

The square root of 21685751 is about 4656.7962162843. The cubic root of 21685751 is about 278.8633812524.

The spelling of 21685751 in words is "twenty-one million, six hundred eighty-five thousand, seven hundred fifty-one".