21561443 has 2 divisors, whose sum is σ = 21561444. Its totient is φ = 21561442.

The previous prime is 21561427. The next prime is 21561469. The reversal of 21561443 is 34416512.

It is an a-pointer prime, because the next prime (21561469) can be obtained adding 21561443 to its sum of digits (26).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21561443 - 2⁴ = 21561427 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21564443) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780721 + 10780722.

It is an arithmetic number, because the mean of its divisors is an integer number (10780722).

Almost surely, 2^21561443 is an apocalyptic number.

21561443 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561443 is an equidigital number, since it uses as much as digits as its factorization.

21561443 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2880, while the sum is 26.

The square root of 21561443 is about 4643.4300899228. The cubic root of 21561443 is about 278.3295223003.

Adding to 21561443 its reverse (34416512), we get a palindrome (55977955).

The spelling of 21561443 in words is "twenty-one million, five hundred sixty-one thousand, four hundred forty-three".