21768457 has 2 divisors, whose sum is σ = 21768458. Its totient is φ = 21768456.

The previous prime is 21768431. The next prime is 21768497. The reversal of 21768457 is 75486712.

It is an a-pointer prime, because the next prime (21768497) can be obtained adding 21768457 to its sum of digits (40).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20466576 + 1301881 = 4524^2 + 1141^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21768457 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21768407) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10884228 + 10884229.

It is an arithmetic number, because the mean of its divisors is an integer number (10884229).

Almost surely, 2^21768457 is an apocalyptic number.

It is an amenable number.

21768457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21768457 is an equidigital number, since it uses as much as digits as its factorization.

21768457 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 94080, while the sum is 40.

The square root of 21768457 is about 4665.6679050271. The cubic root of 21768457 is about 279.2174450243.

The spelling of 21768457 in words is "twenty-one million, seven hundred sixty-eight thousand, four hundred fifty-seven".