21512591 has 2 divisors, whose sum is σ = 21512592. Its totient is φ = 21512590.

The previous prime is 21512539. The next prime is 21512609. The reversal of 21512591 is 19521512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21512591 - 2⁶ = 21512527 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 21512591.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21512501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10756295 + 10756296.

It is an arithmetic number, because the mean of its divisors is an integer number (10756296).

Almost surely, 2^21512591 is an apocalyptic number.

21512591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21512591 is an equidigital number, since it uses as much as digits as its factorization.

21512591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 900, while the sum is 26.

The square root of 21512591 is about 4638.1667714734. The cubic root of 21512591 is about 278.1191585862.

The spelling of 21512591 in words is "twenty-one million, five hundred twelve thousand, five hundred ninety-one".