21665473 has 2 divisors, whose sum is σ = 21665474. Its totient is φ = 21665472.

The previous prime is 21665401. The next prime is 21665489. The reversal of 21665473 is 37456612.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15147664 + 6517809 = 3892^2 + 2553^2 .

It is a cyclic number.

It is not a de Polignac number, because 21665473 - 2²¹ = 19568321 is a prime.

It is equal to p_1369366 and since 21665473 and 1369366 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21665873) 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, 10832736 + 10832737.

It is an arithmetic number, because the mean of its divisors is an integer number (10832737).

Almost surely, 2^21665473 is an apocalyptic number.

It is an amenable number.

21665473 is a deficient number, since it is larger than the sum of its proper divisors (1).

21665473 is an equidigital number, since it uses as much as digits as its factorization.

21665473 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 30240, while the sum is 34.

The square root of 21665473 is about 4654.6184591221. The cubic root of 21665473 is about 278.7764339119.

The spelling of 21665473 in words is "twenty-one million, six hundred sixty-five thousand, four hundred seventy-three".