21002120261 has 2 divisors, whose sum is σ = 21002120262. Its totient is φ = 21002120260.

The previous prime is 21002120257. The next prime is 21002120273. The reversal of 21002120261 is 16202120012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20612057761 + 390062500 = 143569^2 + 19750^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002120261 - 2² = 21002120257 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21002120291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501060130 + 10501060131.

It is an arithmetic number, because the mean of its divisors is an integer number (10501060131).

Almost surely, 2^21002120261 is an apocalyptic number.

It is an amenable number.

21002120261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002120261 is an equidigital number, since it uses as much as digits as its factorization.

21002120261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 17.

Adding to 21002120261 its reverse (16202120012), we get a palindrome (37204240273).

The spelling of 21002120261 in words is "twenty-one billion, two million, one hundred twenty thousand, two hundred sixty-one".