21455557 has 2 divisors, whose sum is σ = 21455558. Its totient is φ = 21455556.

The previous prime is 21455549. The next prime is 21455593. The reversal of 21455557 is 75555412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16008001 + 5447556 = 4001^2 + 2334^2 .

It is a cyclic number.

It is not a de Polignac number, because 21455557 - 2³ = 21455549 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21455537) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10727778 + 10727779.

It is an arithmetic number, because the mean of its divisors is an integer number (10727779).

Almost surely, 2^21455557 is an apocalyptic number.

It is an amenable number.

21455557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21455557 is an equidigital number, since it uses as much as digits as its factorization.

21455557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 35000, while the sum is 34.

The square root of 21455557 is about 4632.0143566271. The cubic root of 21455557 is about 277.8731586704.

The spelling of 21455557 in words is "twenty-one million, four hundred fifty-five thousand, five hundred fifty-seven".