21226021561 has 2 divisors, whose sum is σ = 21226021562. Its totient is φ = 21226021560.

The previous prime is 21226021541. The next prime is 21226021567. The reversal of 21226021561 is 16512062212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15222871161 + 6003150400 = 123381^2 + 77480^2 .

It is a cyclic number.

It is not a de Polignac number, because 21226021561 - 2⁷ = 21226021433 is a prime.

It is not a weakly prime, because it can be changed into another prime (21226021567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10613010780 + 10613010781.

It is an arithmetic number, because the mean of its divisors is an integer number (10613010781).

Almost surely, 2^21226021561 is an apocalyptic number.

It is an amenable number.

21226021561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21226021561 is an equidigital number, since it uses as much as digits as its factorization.

21226021561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2880, while the sum is 28.

Adding to 21226021561 its reverse (16512062212), we get a palindrome (37738083773).

The spelling of 21226021561 in words is "twenty-one billion, two hundred twenty-six million, twenty-one thousand, five hundred sixty-one".