21278 has 4 divisors (see below), whose sum is σ = 31920. Its totient is φ = 10638.

The previous prime is 21277. The next prime is 21283. The reversal of 21278 is 87212.

It is a semiprime because it is the product of two primes.

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

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21277) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5318 + ... + 5321.

It is an arithmetic number, because the mean of its divisors is an integer number (7980).

2²¹²⁷⁸ is an apocalyptic number.

21278 is a deficient number, since it is larger than the sum of its proper divisors (10642).

21278 is a wasteful number, since it uses less digits than its factorization.

21278 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10641.

The product of its digits is 224, while the sum is 20.

The square root of 21278 is about 145.8698049632. The cubic root of 21278 is about 27.7104514684.

It can be divided in two parts, 2 and 1278, that multiplied together give a triangular number (2556 = T₇₁).

The spelling of 21278 in words is "twenty-one thousand, two hundred seventy-eight".