• 69 can be written using four 4's:
69 has 4 divisors (see below), whose sum is σ = 96. Its totient is φ = 44.
The previous prime is 67. The next prime is 71. The reversal of 69 is 96.
69 is an esthetic number in base 5, base 9, base 13 and base 16, because in such bases its adjacent digits differ by 1.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.
It is an interprime number because it is at equal distance from previous prime (67) and next prime (71).
It is a cyclic number.
It is not a de Polignac number, because 69 - 21 = 67 is a prime.
It is a super-2 number, since 2×692 = 9522, which contains 22 as substring.
It is an Ulam number.
It is a D-number.
It is an alternating number because its digits alternate between even and odd.
69 is a strobogrammatic number because it is the same when read upside-down.
69 is a modest number, since divided by 9 gives 6 as remainder.
It is a Curzon number.
69 is a lucky number.
It is a plaindrome in base 5, base 7, base 10, base 12, base 14, base 15 and base 16.
It is a nialpdrome in base 9, base 11 and base 13.
It is a congruent number.
It is a panconsummate number.
It is a pernicious number, because its binary representation contains a prime number (3) of ones.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9 + ... + 14.
It is an arithmetic number, because the mean of its divisors is an integer number (24).
It is an amenable number.
69 is a deficient number, since it is larger than the sum of its proper divisors (27).
69 is a wasteful number, since it uses less digits than its factorization.
69 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 26.
The product of its digits is 54, while the sum is 15.
The square root of 69 is about 8.3066238629. The cubic root of 69 is about 4.1015659297.
Multiplying 69 by its sum of digits (15), we get a triangular number (1035 = T45).
Subtracting from 69 its product of digits (54), we obtain a triangular number (15 = T5).
Subtracting 69 from its reverse (96), we obtain a cube (27 = 33).
The spelling of 69 in words is "sixty-nine", and thus it is an aban number, an oban number, and an uban number.
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