75

75 = 3 × 5 × 5

75 = 12 × 3 + 4 + 5 + 6 + 7 + 8 + 9

75 = 9 + 8 + 7 × 6 + 5 + 4 + 3 × 2 + 1

75 = 0^6 + 1^9 − 2^8 − 3^7 + 4^5 + 5^3 + 6^4 + 7^1 + 8^2 + 9^0

75 = 2 576 191 140 760³ + 1 217 343 443 218³ − 2 663 786 047 493³
75 =59 897 299 698 355³ − 47 258 398 396 091³ − 47 819 328 945 509³

Number k such that the Woodall number kx2^k - 1 is prime

Keith number or Repfigit (Repetitive Fibonacci-like digit)

a(n) = (2*n - 1)*(7*n^2 - 7*n + 3)/3. n=3

Factors: 1, 3, 5, 15, 25, 75

Seventy-five

Representations, Binary to Hexadecimal:

1001011_2
2210_3
1023_4
300_5
203_6
135_7
113_8
83_9
69_11
63_12
5a_13
55_14
50_15
4b_16

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