16501421221 has 2 divisors, whose sum is σ = 16501421222. Its totient is φ = 16501421220.

The previous prime is 16501421201. The next prime is 16501421227. The reversal of 16501421221 is 12212410561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14716358721 + 1785062500 = 121311^2 + 42250^2 .

It is a cyclic number.

It is not a de Polignac number, because 16501421221 - 2¹³ = 16501413029 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16501421227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8250710610 + 8250710611.

It is an arithmetic number, because the mean of its divisors is an integer number (8250710611).

Almost surely, 2^16501421221 is an apocalyptic number.

It is an amenable number.

16501421221 is a deficient number, since it is larger than the sum of its proper divisors (1).

16501421221 is an equidigital number, since it uses as much as digits as its factorization.

16501421221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 960, while the sum is 25.

Adding to 16501421221 its reverse (12212410561), we get a palindrome (28713831782).

The spelling of 16501421221 in words is "sixteen billion, five hundred one million, four hundred twenty-one thousand, two hundred twenty-one".