21661597 has 2 divisors, whose sum is σ = 21661598. Its totient is φ = 21661596.

The previous prime is 21661583. The next prime is 21661609. The reversal of 21661597 is 79516612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13883076 + 7778521 = 3726^2 + 2789^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661597 - 2¹⁵ = 21628829 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661517) 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, 10830798 + 10830799.

It is an arithmetic number, because the mean of its divisors is an integer number (10830799).

Almost surely, 2^21661597 is an apocalyptic number.

It is an amenable number.

21661597 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661597 is an equidigital number, since it uses as much as digits as its factorization.

21661597 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 22680, while the sum is 37.

The square root of 21661597 is about 4654.2020798414. The cubic root of 21661597 is about 278.7598083513.

The spelling of 21661597 in words is "twenty-one million, six hundred sixty-one thousand, five hundred ninety-seven".