21512749 has 2 divisors, whose sum is σ = 21512750. Its totient is φ = 21512748.

The previous prime is 21512747. The next prime is 21512759. The reversal of 21512749 is 94721512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14303524 + 7209225 = 3782^2 + 2685^2 .

It is a cyclic number.

It is not a de Polignac number, because 21512749 - 2¹ = 21512747 is a prime.

Together with 21512747, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21512749.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21512747) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10756374 + 10756375.

It is an arithmetic number, because the mean of its divisors is an integer number (10756375).

Almost surely, 2^21512749 is an apocalyptic number.

It is an amenable number.

21512749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21512749 is an equidigital number, since it uses as much as digits as its factorization.

21512749 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5040, while the sum is 31.

The square root of 21512749 is about 4638.1838040336. The cubic root of 21512749 is about 278.1198394700.

It can be divided in two parts, 2151 and 2749, that added together give a square (4900 = 70²).

The spelling of 21512749 in words is "twenty-one million, five hundred twelve thousand, seven hundred forty-nine".