21009679 has 2 divisors, whose sum is σ = 21009680. Its totient is φ = 21009678.

The previous prime is 21009643. The next prime is 21009683. The reversal of 21009679 is 97690012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21009679 - 2⁹ = 21009167 is a prime.

It is a super-2 number, since 2×21009679² = 882813223366082, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21009629) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504839 + 10504840.

It is an arithmetic number, because the mean of its divisors is an integer number (10504840).

Almost surely, 2^21009679 is an apocalyptic number.

21009679 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009679 is an equidigital number, since it uses as much as digits as its factorization.

21009679 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6804, while the sum is 34.

The square root of 21009679 is about 4583.6316387773. The cubic root of 21009679 is about 275.9347978374.

The spelling of 21009679 in words is "twenty-one million, nine thousand, six hundred seventy-nine".