21518647717121 has 2 divisors, whose sum is σ = 21518647717122. Its totient is φ = 21518647717120.

The previous prime is 21518647717087. The next prime is 21518647717139. The reversal of 21518647717121 is 12171774681512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18509879940721 + 3008767776400 = 4302311^2 + 1734580^2 .

It is a cyclic number.

It is not a de Polignac number, because 21518647717121 - 2¹⁸ = 21518647454977 is a prime.

It is not a weakly prime, because it can be changed into another prime (21518647717921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10759323858560 + 10759323858561.

It is an arithmetic number, because the mean of its divisors is an integer number (10759323858561).

Almost surely, 2^{21518647717121} is an apocalyptic number.

It is an amenable number.

21518647717121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21518647717121 is an equidigital number, since it uses as much as digits as its factorization.

21518647717121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1317120, while the sum is 53.

The spelling of 21518647717121 in words is "twenty-one trillion, five hundred eighteen billion, six hundred forty-seven million, seven hundred seventeen thousand, one hundred twenty-one".