21043261 has 2 divisors, whose sum is σ = 21043262. Its totient is φ = 21043260.

The previous prime is 21043259. The next prime is 21043271. The reversal of 21043261 is 16234012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16048036 + 4995225 = 4006^2 + 2235^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043261 - 2¹ = 21043259 is a prime.

Together with 21043259, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21043271) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521630 + 10521631.

It is an arithmetic number, because the mean of its divisors is an integer number (10521631).

Almost surely, 2^21043261 is an apocalyptic number.

21043261 is the 2052-nd centered decagonal number.

It is an amenable number.

21043261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21043261 is an equidigital number, since it uses as much as digits as its factorization.

21043261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21043261 is about 4587.2934285916. The cubic root of 21043261 is about 276.0817382005.

Adding to 21043261 its reverse (16234012), we get a palindrome (37277273).

Subtracting from 21043261 its reverse (16234012), we obtain a square (4809249 = 2193²).

The spelling of 21043261 in words is "twenty-one million, forty-three thousand, two hundred sixty-one".