121721551 has 4 divisors (see below), whose sum is σ = 139110352. Its totient is φ = 104332752.

The previous prime is 121721539. The next prime is 121721591. The reversal of 121721551 is 155127121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 155127121 = 241 ⋅643681.

It is a cyclic number.

It is not a de Polignac number, because 121721551 - 2¹³ = 121713359 is a prime.

It is a super-2 number, since 2×121721551² = 29632271955691202, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (121721591) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8694390 + ... + 8694403.

It is an arithmetic number, because the mean of its divisors is an integer number (34777588).

Almost surely, 2^121721551 is an apocalyptic number.

121721551 is a deficient number, since it is larger than the sum of its proper divisors (17388801).

121721551 is an equidigital number, since it uses as much as digits as its factorization.

121721551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17388800.

The product of its digits is 700, while the sum is 25.

The square root of 121721551 is about 11032.7490227957. The cubic root of 121721551 is about 495.5899519781.

Adding to 121721551 its reverse (155127121), we get a palindrome (276848672).

The spelling of 121721551 in words is "one hundred twenty-one million, seven hundred twenty-one thousand, five hundred fifty-one".