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A141603
Odd composites of the form n-(p(n+2)-p(n))/(p(n+1)-p(n-1)), where p(n)=n-th prime.
1
9, 21, 25, 27, 33, 63, 77, 81, 93, 105, 125, 143, 147, 153, 165, 171, 175, 185, 235, 243, 247, 249, 255, 273, 285, 301, 321, 335, 345, 363, 405, 437, 473, 475, 483, 517, 529, 533, 559, 567, 579, 585, 591, 603, 627, 671, 689, 711, 767, 789, 793, 825, 861, 873, 891, 897
OFFSET
1,1
COMMENTS
Entries are not repeated and shown in natural order.
LINKS
EXAMPLE
n=10: 10-(37-29)/(31-23)=9=a(1).
n=22: 22-(89-79)/(83-73)=21=a(2).
n=26: 26-(107-101)/(103-97)=25=a(3).
n=28: 28-(113-107)/(109-103)=27=a(4).
n=34: 34-(151-139)/(149-137)=33=a(5).
MATHEMATICA
f[{a_, b_, c_, d_}]:=(d-b)/(c-a); Select[Table[n-f[Prime[Range[n-1, n+2]]], {n, 2, 1000}], OddQ[#]&&CompositeQ[#]&]//Union (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 15 2018 *)
CROSSREFS
Cf. A000040.
Sequence in context: A067887 A345330 A174870 * A262748 A138786 A305733
KEYWORD
nonn
AUTHOR
EXTENSIONS
Corrected and extended by R. J. Mathar, Sep 26 2008
STATUS
approved