21003432581 has 2 divisors, whose sum is σ = 21003432582. Its totient is φ = 21003432580.

The previous prime is 21003432421. The next prime is 21003432589. The reversal of 21003432581 is 18523430012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18444084481 + 2559348100 = 135809^2 + 50590^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003432581 - 2²⁶ = 20936323717 is a prime.

It is a super-2 number, since 2×21003432581² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21003432589) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501716290 + 10501716291.

It is an arithmetic number, because the mean of its divisors is an integer number (10501716291).

Almost surely, 2^21003432581 is an apocalyptic number.

It is an amenable number.

21003432581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21003432581 is an equidigital number, since it uses as much as digits as its factorization.

21003432581 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5760, while the sum is 29.

Adding to 21003432581 its reverse (18523430012), we get a palindrome (39526862593).

The spelling of 21003432581 in words is "twenty-one billion, three million, four hundred thirty-two thousand, five hundred eighty-one".