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A145021 a(n) = number of different positive integers that can be formed from different groupings of expressions of the form n op1 n op2 n op3 n, where each of op1, op2 and op3 are addition, subtraction, multiplication or division. 0
4, 10, 20, 25, 27, 29, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If one uses all 4^3=64 forms of this type but no parentheses, the sequence starts 4,9,15,13,15,14... In this case 4/4/4/4=1/4/4=1/16 is not an integer (association left-to-right), whereas with parenthesis one could write (4/4)/(4/4)=1, an integer, for example. The definition need clarification in this respect. [From R. J. Mathar, Jan 22 2009]

LINKS

Table of n, a(n) for n=1..65.

FORMULA

If k >3, a(2k-1)=30 and a(2k)=31. - Ken Levasseur, Oct 01 2008

EXAMPLE

You can form the numbers 1, 2, 3, 4 with 4 ones; hence the first term is 4.

CROSSREFS

Sequence in context: A268221 A086176 A015789 * A135280 A100436 A009882

Adjacent sequences:  A145018 A145019 A145020 * A145022 A145023 A145024

KEYWORD

easy,nonn

AUTHOR

Ken Levasseur, Sep 29 2008

STATUS

approved

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Last modified October 23 20:10 EDT 2017. Contains 293813 sequences.