21455257 has 2 divisors, whose sum is σ = 21455258. Its totient is φ = 21455256.

The previous prime is 21455183. The next prime is 21455261. The reversal of 21455257 is 75255412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17007376 + 4447881 = 4124^2 + 2109^2 .

It is a cyclic number.

It is not a de Polignac number, because 21455257 - 2¹⁹ = 20930969 is a prime.

It is not a weakly prime, because it can be changed into another prime (21455557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10727628 + 10727629.

It is an arithmetic number, because the mean of its divisors is an integer number (10727629).

Almost surely, 2^21455257 is an apocalyptic number.

It is an amenable number.

21455257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21455257 is an equidigital number, since it uses as much as digits as its factorization.

21455257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14000, while the sum is 31.

The square root of 21455257 is about 4631.9819731946. The cubic root of 21455257 is about 277.8718635539.

It can be divided in two parts, 21455 and 257, that added together give a palindrome (21712).

The spelling of 21455257 in words is "twenty-one million, four hundred fifty-five thousand, two hundred fifty-seven".