21661465732391 has 2 divisors, whose sum is σ = 21661465732392. Its totient is φ = 21661465732390.

The previous prime is 21661465732369. The next prime is 21661465732429. The reversal of 21661465732391 is 19323756416612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21661465732391 - 2⁶ = 21661465732327 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661465732331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830732866195 + 10830732866196.

It is an arithmetic number, because the mean of its divisors is an integer number (10830732866196).

Almost surely, 2^{21661465732391} is an apocalyptic number.

21661465732391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661465732391 is an equidigital number, since it uses as much as digits as its factorization.

21661465732391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9797760, while the sum is 56.

The spelling of 21661465732391 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred sixty-five million, seven hundred thirty-two thousand, three hundred ninety-one".