21388751 has 2 divisors, whose sum is σ = 21388752. Its totient is φ = 21388750.

The previous prime is 21388723. The next prime is 21388769. The reversal of 21388751 is 15788312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21388751 - 2⁶ = 21388687 is a prime.

It is a Sophie Germain prime.

It is equal to p_1352987 and since 21388751 and 1352987 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21388721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10694375 + 10694376.

It is an arithmetic number, because the mean of its divisors is an integer number (10694376).

Almost surely, 2^21388751 is an apocalyptic number.

21388751 is a deficient number, since it is larger than the sum of its proper divisors (1).

21388751 is an equidigital number, since it uses as much as digits as its factorization.

21388751 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13440, while the sum is 35.

The square root of 21388751 is about 4624.7974009680. The cubic root of 21388751 is about 277.5844549911.

The spelling of 21388751 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred fifty-one".