21240343261 has 2 divisors, whose sum is σ = 21240343262. Its totient is φ = 21240343260.

The previous prime is 21240343217. The next prime is 21240343297. The reversal of 21240343261 is 16234304212.

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., 15751756036 + 5488587225 = 125506^2 + 74085^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21240343261 is a prime.

It is a super-2 number, since 2×21240343261² (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 (21240343361) 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, 10620171630 + 10620171631.

It is an arithmetic number, because the mean of its divisors is an integer number (10620171631).

Almost surely, 2^21240343261 is an apocalyptic number.

It is an amenable number.

21240343261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21240343261 is an equidigital number, since it uses as much as digits as its factorization.

21240343261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6912, while the sum is 28.

Adding to 21240343261 its reverse (16234304212), we get a palindrome (37474647473).

The spelling of 21240343261 in words is "twenty-one billion, two hundred forty million, three hundred forty-three thousand, two hundred sixty-one".