21771251 has 2 divisors, whose sum is σ = 21771252. Its totient is φ = 21771250.

The previous prime is 21771247. The next prime is 21771307. The reversal of 21771251 is 15217712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21771251 - 2² = 21771247 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21771251.

It is not a weakly prime, because it can be changed into another prime (21771221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10885625 + 10885626.

It is an arithmetic number, because the mean of its divisors is an integer number (10885626).

Almost surely, 2^21771251 is an apocalyptic number.

21771251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21771251 is an equidigital number, since it uses as much as digits as its factorization.

21771251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 980, while the sum is 26.

The square root of 21771251 is about 4665.9673166451. The cubic root of 21771251 is about 279.2293904455.

Adding to 21771251 its reverse (15217712), we get a palindrome (36988963).

It can be divided in two parts, 21771 and 251, that added together give a palindrome (22022).

The spelling of 21771251 in words is "twenty-one million, seven hundred seventy-one thousand, two hundred fifty-one".