21670 has 16 divisors (see below), whose sum is σ = 42768. Its totient is φ = 7840.

The previous prime is 21661. The next prime is 21673. The reversal of 21670 is 7612.

21670 = T₅₄ + T₅₅ + ... + T₆₅.

It is an alternating number because its digits alternate between even and odd.

21670 is an undulating number in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21673) by changing a digit.

21670 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12 + ... + 208.

It is an arithmetic number, because the mean of its divisors is an integer number (2673).

2²¹⁶⁷⁰ is an apocalyptic number.

21670 is a deficient number, since it is larger than the sum of its proper divisors (21098).

21670 is a wasteful number, since it uses less digits than its factorization.

21670 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 215.

The product of its (nonzero) digits is 84, while the sum is 16.

The square root of 21670 is about 147.2073367737. The cubic root of 21670 is about 27.8795849336.

The spelling of 21670 in words is "twenty-one thousand, six hundred seventy".