21281261 has 2 divisors, whose sum is σ = 21281262. Its totient is φ = 21281260.

The previous prime is 21281251. The next prime is 21281321. The reversal of 21281261 is 16218212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19307236 + 1974025 = 4394^2 + 1405^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21281261 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21281201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10640630 + 10640631.

It is an arithmetic number, because the mean of its divisors is an integer number (10640631).

Almost surely, 2^21281261 is an apocalyptic number.

It is an amenable number.

21281261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21281261 is an equidigital number, since it uses as much as digits as its factorization.

21281261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 384, while the sum is 23.

The square root of 21281261 is about 4613.1617140525. The cubic root of 21281261 is about 277.1186700192.

Adding to 21281261 its reverse (16218212), we get a palindrome (37499473).

The spelling of 21281261 in words is "twenty-one million, two hundred eighty-one thousand, two hundred sixty-one".