21158261 has 2 divisors, whose sum is σ = 21158262. Its totient is φ = 21158260.

The previous prime is 21158257. The next prime is 21158273. The reversal of 21158261 is 16285112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14938225 + 6220036 = 3865^2 + 2494^2 .

It is a cyclic number.

It is not a de Polignac number, because 21158261 - 2² = 21158257 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21158261.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21158201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10579130 + 10579131.

It is an arithmetic number, because the mean of its divisors is an integer number (10579131).

Almost surely, 2^21158261 is an apocalyptic number.

It is an amenable number.

21158261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21158261 is an equidigital number, since it uses as much as digits as its factorization.

21158261 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 960, while the sum is 26.

The square root of 21158261 is about 4599.8109743771. The cubic root of 21158261 is about 276.5837475095.

The spelling of 21158261 in words is "twenty-one million, one hundred fifty-eight thousand, two hundred sixty-one".