21606817 has 2 divisors, whose sum is σ = 21606818. Its totient is φ = 21606816.

The previous prime is 21606787. The next prime is 21606839. The reversal of 21606817 is 71860612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19368801 + 2238016 = 4401^2 + 1496^2 .

It is a cyclic number.

It is not a de Polignac number, because 21606817 - 2²³ = 13218209 is a prime.

It is not a weakly prime, because it can be changed into another prime (21606217) 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, 10803408 + 10803409.

It is an arithmetic number, because the mean of its divisors is an integer number (10803409).

Almost surely, 2^21606817 is an apocalyptic number.

It is an amenable number.

21606817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21606817 is an equidigital number, since it uses as much as digits as its factorization.

21606817 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21606817 is about 4648.3133500228. The cubic root of 21606817 is about 278.5246248158.

The spelling of 21606817 in words is "twenty-one million, six hundred six thousand, eight hundred seventeen".