21417257 has 2 divisors, whose sum is σ = 21417258. Its totient is φ = 21417256.

The previous prime is 21417239. The next prime is 21417269. The reversal of 21417257 is 75271412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20939776 + 477481 = 4576^2 + 691^2 .

It is a cyclic number.

It is not a de Polignac number, because 21417257 - 2¹⁶ = 21351721 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21414257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10708628 + 10708629.

It is an arithmetic number, because the mean of its divisors is an integer number (10708629).

Almost surely, 2^21417257 is an apocalyptic number.

It is an amenable number.

21417257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21417257 is an equidigital number, since it uses as much as digits as its factorization.

21417257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3920, while the sum is 29.

The square root of 21417257 is about 4627.8782395392. The cubic root of 21417257 is about 277.7077177564.

Adding to 21417257 its reverse (75271412), we get a palindrome (96688669).

It can be divided in two parts, 214 and 17257, that added together give a palindrome (17471).

The spelling of 21417257 in words is "twenty-one million, four hundred seventeen thousand, two hundred fifty-seven".