21000431261 has 2 divisors, whose sum is σ = 21000431262. Its totient is φ = 21000431260.

The previous prime is 21000431213. The next prime is 21000431299. The reversal of 21000431261 is 16213400012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15613752025 + 5386679236 = 124955^2 + 73394^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21000431261 is a prime.

It is a super-2 number, since 2×21000431261² (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 (21000431201) 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, 10500215630 + 10500215631.

It is an arithmetic number, because the mean of its divisors is an integer number (10500215631).

Almost surely, 2^21000431261 is an apocalyptic number.

It is an amenable number.

21000431261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000431261 is an equidigital number, since it uses as much as digits as its factorization.

21000431261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 20.

Adding to 21000431261 its reverse (16213400012), we get a palindrome (37213831273).

The spelling of 21000431261 in words is "twenty-one billion, four hundred thirty-one thousand, two hundred sixty-one".