21461581 has 2 divisors, whose sum is σ = 21461582. Its totient is φ = 21461580.

The previous prime is 21461551. The next prime is 21461593. The reversal of 21461581 is 18516412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20340100 + 1121481 = 4510^2 + 1059^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21461581 is a prime.

It is a super-2 number, since 2×21461581² = 921198918039122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21461521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10730790 + 10730791.

It is an arithmetic number, because the mean of its divisors is an integer number (10730791).

Almost surely, 2^21461581 is an apocalyptic number.

It is an amenable number.

21461581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21461581 is an equidigital number, since it uses as much as digits as its factorization.

21461581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1920, while the sum is 28.

The square root of 21461581 is about 4632.6645680429. The cubic root of 21461581 is about 277.8991620545.

Adding to 21461581 its reverse (18516412), we get a palindrome (39977993).

The spelling of 21461581 in words is "twenty-one million, four hundred sixty-one thousand, five hundred eighty-one".