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75 (number)

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(Redirected from Seventy-five) Natural number
← 74 75 76 →
70 71 72 73 74 75 76 77 78 79 0 10 20 30 40 50 60 70 80 90
Cardinalseventy-five
Ordinal75th
(seventy-fifth)
Factorization3 × 5
Divisors1, 3, 5, 15, 25, 75
Greek numeralΟΕ´
Roman numeralLXXV, lxxv
Binary10010112
Ternary22103
Senary2036
Octal1138
Duodecimal6312
Hexadecimal4B16

75 (seventy-five) is the natural number following 74 and preceding 76.

In mathematics

75 is a self number because there is no integer that added up to its own digits adds up to 75. It is the sum of the first five pentagonal numbers, and therefore a pentagonal pyramidal number, as well as a nonagonal number.

It is also the fourth ordered Bell number, and a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 7, 5, 12, 17, 29, 46, 75...

75 is the count of the number of weak orderings on a set of four items.

Excluding the infinite sets, there are 75 uniform polyhedra in the third dimension, which incorporate star polyhedra as well. Inclusive of 7 families of prisms and antiprisms, there are also 75 uniform compound polyhedra.

References

  1. Sloane, N. J. A. (ed.). "Sequence A003052". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  2. Sloane, N. J. A. (ed.). "Sequence A001106". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  3. Sloane, N. J. A. (ed.). "Sequence A002411". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  4. Sloane, N. J. A. (ed.). "Sequence A007629". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  5. Sloane, N. J. A. (ed.). "Sequence A000670". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
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