21685961 has 4 divisors (see below), whose sum is σ = 23657424. Its totient is φ = 19714500.

The previous prime is 21685913. The next prime is 21685967. The reversal of 21685961 is 16958612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21685961 - 2¹⁰ = 21684937 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21685967) 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 3 ways as a sum of consecutive naturals, for example, 985715 + ... + 985736.

It is an arithmetic number, because the mean of its divisors is an integer number (5914356).

Almost surely, 2^21685961 is an apocalyptic number.

It is an amenable number.

21685961 is a deficient number, since it is larger than the sum of its proper divisors (1971463).

21685961 is a wasteful number, since it uses less digits than its factorization.

21685961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1971462.

The product of its digits is 25920, while the sum is 38.

The square root of 21685961 is about 4656.8187639203. The cubic root of 21685961 is about 278.8642813999.

The spelling of 21685961 in words is "twenty-one million, six hundred eighty-five thousand, nine hundred sixty-one".