21610681 has 2 divisors, whose sum is σ = 21610682. Its totient is φ = 21610680.

The previous prime is 21610669. The next prime is 21610691. The reversal of 21610681 is 18601612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18352656 + 3258025 = 4284^2 + 1805^2 .

It is a cyclic number.

It is not a de Polignac number, because 21610681 - 2¹³ = 21602489 is a prime.

It is a super-2 number, since 2×21610681² = 934043066567522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21610661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805340 + 10805341.

It is an arithmetic number, because the mean of its divisors is an integer number (10805341).

Almost surely, 2^21610681 is an apocalyptic number.

It is an amenable number.

21610681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21610681 is an equidigital number, since it uses as much as digits as its factorization.

21610681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21610681 is about 4648.7289660723. The cubic root of 21610681 is about 278.5412269064.

The spelling of 21610681 in words is "twenty-one million, six hundred ten thousand, six hundred eighty-one".