21013031261 has 2 divisors, whose sum is σ = 21013031262. Its totient is φ = 21013031260.

The previous prime is 21013031257. The next prime is 21013031267. The reversal of 21013031261 is 16213031012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19844075161 + 1168956100 = 140869^2 + 34190^2 .

It is a cyclic number.

It is not a de Polignac number, because 21013031261 - 2² = 21013031257 is a prime.

It is a super-4 number, since 4×21013031261⁴ (a number of 42 digits) contains 4444 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21013031267) 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, 10506515630 + 10506515631.

It is an arithmetic number, because the mean of its divisors is an integer number (10506515631).

Almost surely, 2^21013031261 is an apocalyptic number.

It is an amenable number.

21013031261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21013031261 is an equidigital number, since it uses as much as digits as its factorization.

21013031261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 20.

Adding to 21013031261 its reverse (16213031012), we get a palindrome (37226062273).

The spelling of 21013031261 in words is "twenty-one billion, thirteen million, thirty-one thousand, two hundred sixty-one".