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A028389
The 5x + 1 sequence beginning at 7.
1
7, 36, 18, 9, 46, 23, 116, 58, 29, 146, 73, 366, 183, 916, 458, 229, 1146, 573, 2866, 1433, 7166, 3583, 17916, 8958, 4479, 22396, 11198, 5599, 27996, 13998, 6999, 34996, 17498, 8749, 43746, 21873, 109366, 54683, 273416, 136708, 68354, 34177, 170886, 85443, 427216
OFFSET
0,1
LINKS
FORMULA
a(0) = 7; a(n) = 5*a(n-1) + 1 if a(n-1) is odd, a(n) = a(n-1)/2 otherwise.
MAPLE
f := proc(n) option remember; if n = 0 then 7 elif f(n-1) mod 2 = 0 then f(n-1)/2 else 5*f(n-1)+1; fi; end; seq(f(n), n=0..50);
MATHEMATICA
a[0] = 7; a[n_] := a[n] = If[OddQ[a[n-1]], 5 a[n-1] + 1, a[n-1]/2];
a /@ Range[0, 50] (* Jean-François Alcover, Nov 03 2020 *)
NestList[If[OddQ[#], 5#+1, #/2]&, 7, 50] (* Harvey P. Dale, Nov 03 2022 *)
CROSSREFS
KEYWORD
nonn
EXTENSIONS
Named edited by Andrew Howroyd, Aug 21 2020
STATUS
approved