21661287313 has 2 divisors, whose sum is σ = 21661287314. Its totient is φ = 21661287312.

The previous prime is 21661287311. The next prime is 21661287359. The reversal of 21661287313 is 31378216612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16668875664 + 4992411649 = 129108^2 + 70657^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661287313 - 2¹ = 21661287311 is a prime.

It is a super-2 number, since 2×21661287313² (a number of 21 digits) contains 22 as substring.

Together with 21661287311, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21661287311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830643656 + 10830643657.

It is an arithmetic number, because the mean of its divisors is an integer number (10830643657).

Almost surely, 2^21661287313 is an apocalyptic number.

It is an amenable number.

21661287313 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661287313 is an equidigital number, since it uses as much as digits as its factorization.

21661287313 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72576, while the sum is 40.

The spelling of 21661287313 in words is "twenty-one billion, six hundred sixty-one million, two hundred eighty-seven thousand, three hundred thirteen".