21026 has 4 divisors (see below), whose sum is σ = 31542. Its totient is φ = 10512.

The previous prime is 21023. The next prime is 21031. The reversal of 21026 is 62012.

It is a Cunningham number, because it is equal to 145²+1.

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

It can be written as a sum of positive squares in only one way, i.e., 21025 + 1 = 145^2 + 1^2 .

It is a nialpdrome in base 13 and base 16.

It is a junction number, because it is equal to n+sod(n) for n = 20998 and 21016.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21023) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5255 + ... + 5258.

2²¹⁰²⁶ is an apocalyptic number.

21026 is a deficient number, since it is larger than the sum of its proper divisors (10516).

21026 is a wasteful number, since it uses less digits than its factorization.

21026 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10515.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21026 is about 145.0034482349. The cubic root of 21026 is about 27.6006231043.

Adding to 21026 its reverse (62012), we get a palindrome (83038).

It can be divided in two parts, 210 and 26, that multiplied together give a triangular number (5460 = T₁₀₄).

The spelling of 21026 in words is "twenty-one thousand, twenty-six".