21157117 has 2 divisors, whose sum is σ = 21157118. Its totient is φ = 21157116.

The previous prime is 21157111. The next prime is 21157121. The reversal of 21157117 is 71175112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20169081 + 988036 = 4491^2 + 994^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157117 - 2¹⁵ = 21124349 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21157091 and 21157100.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21157111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578558 + 10578559.

It is an arithmetic number, because the mean of its divisors is an integer number (10578559).

Almost surely, 2^21157117 is an apocalyptic number.

It is an amenable number.

21157117 is a deficient number, since it is larger than the sum of its proper divisors (1).

21157117 is an equidigital number, since it uses as much as digits as its factorization.

21157117 is an evil number, because the sum of its binary digits is even.

The product of its digits is 490, while the sum is 25.

The square root of 21157117 is about 4599.6866197601. The cubic root of 21157117 is about 276.5787625770.

The spelling of 21157117 in words is "twenty-one million, one hundred fifty-seven thousand, one hundred seventeen".