21001211261 has 2 divisors, whose sum is σ = 21001211262. Its totient is φ = 21001211260.

The previous prime is 21001211111. The next prime is 21001211269. The reversal of 21001211261 is 16211210012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16032371161 + 4968840100 = 126619^2 + 70490^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001211261 - 2¹⁸ = 21000949117 is a prime.

It is a super-3 number, since 3×21001211261³ (a number of 32 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001211269) 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, 10500605630 + 10500605631.

It is an arithmetic number, because the mean of its divisors is an integer number (10500605631).

Almost surely, 2^21001211261 is an apocalyptic number.

It is an amenable number.

21001211261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001211261 is an equidigital number, since it uses as much as digits as its factorization.

21001211261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48, while the sum is 17.

Adding to 21001211261 its reverse (16211210012), we get a palindrome (37212421273).

The spelling of 21001211261 in words is "twenty-one billion, one million, two hundred eleven thousand, two hundred sixty-one".