21111010121261 has 2 divisors, whose sum is σ = 21111010121262. Its totient is φ = 21111010121260.

The previous prime is 21111010121219. The next prime is 21111010121273. The reversal of 21111010121261 is 16212101011112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19598063380900 + 1512946740361 = 4426970^2 + 1230019^2 .

It is a cyclic number.

It is not a de Polignac number, because 21111010121261 - 2¹⁰ = 21111010120237 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21111010121281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555505060630 + 10555505060631.

It is an arithmetic number, because the mean of its divisors is an integer number (10555505060631).

Almost surely, 2^{21111010121261} is an apocalyptic number.

It is an amenable number.

21111010121261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111010121261 is an equidigital number, since it uses as much as digits as its factorization.

21111010121261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48, while the sum is 20.

Adding to 21111010121261 its reverse (16212101011112), we get a palindrome (37323111132373).

The spelling of 21111010121261 in words is "twenty-one trillion, one hundred eleven billion, ten million, one hundred twenty-one thousand, two hundred sixty-one".