21506633390261 has 2 divisors, whose sum is σ = 21506633390262. Its totient is φ = 21506633390260.

The previous prime is 21506633390251. The next prime is 21506633390279. The reversal of 21506633390261 is 16209333660512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18018072352900 + 3488561037361 = 4244770^2 + 1867769^2 .

It is a cyclic number.

It is not a de Polignac number, because 21506633390261 - 2⁶ = 21506633390197 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21506633390251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10753316695130 + 10753316695131.

It is an arithmetic number, because the mean of its divisors is an integer number (10753316695131).

Almost surely, 2^{21506633390261} is an apocalyptic number.

It is an amenable number.

21506633390261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21506633390261 is an equidigital number, since it uses as much as digits as its factorization.

21506633390261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1049760, while the sum is 47.

The spelling of 21506633390261 in words is "twenty-one trillion, five hundred six billion, six hundred thirty-three million, three hundred ninety thousand, two hundred sixty-one".