21654908491 has 2 divisors, whose sum is σ = 21654908492. Its totient is φ = 21654908490.

The previous prime is 21654908479. The next prime is 21654908573. The reversal of 21654908491 is 19480945612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21654908491 - 2⁹ = 21654907979 is a prime.

It is not a weakly prime, because it can be changed into another prime (21654908461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10827454245 + 10827454246.

It is an arithmetic number, because the mean of its divisors is an integer number (10827454246).

Almost surely, 2^21654908491 is an apocalyptic number.

21654908491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21654908491 is an equidigital number, since it uses as much as digits as its factorization.

21654908491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 622080, while the sum is 49.

It can be divided in two parts, 2165 and 4908491, that added together give a square (4910656 = 2216²).

The spelling of 21654908491 in words is "twenty-one billion, six hundred fifty-four million, nine hundred eight thousand, four hundred ninety-one".