This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
isok(n,s=12)={for(k=0, s, my(r=fromdigits(Vecrev(binary(n)),2)); if(r==n, return(k==s)); n += r); 0} \\ Andrew Howroyd, Dec 05 2024
17 (decimal) = 122 -> 122 + 221 = 1120 -> 1120 + 211 = 2101 -> 2101 + 1012 = 10120 -> 10120 + 2101 = 12221 (palindrome) = 160 (decimal) requires 4 steps, so a(17) = 4.
m := 120; stop := 1000; for n := 0 to m do v := -1; c := 0; k := n; while c < stop do d := k; rev := 0; while d > 0 do rev := 3*rev + (d mod 3); d := d div 3; end; if k = rev then v := c; c := stop; else inc(c); k := k + rev; end; end; write(v,","); end;
5 is the smallest number which requires two steps to reach a base 3 palindrome (cf. A066057), so a(2) = 5; 5 (decimal) = 12 -> 12 + 21 = 110 -> 110 + 011 = 121 (palindrome) = 16 (decimal).
var ar: array; end; m := 45; ar := alloc(array, m+1, -1); mc := m+1; n := 0; while mc > 0 do v := -1; c := 0; k := n; while c < m+1 do d := k; rev := 0; while d > 0 do rev := 3*rev+(d mod 3); d := d div 3; end; if k = rev then v := c; c := m+1; else inc(c); k := k+rev; end; end; if 0 <= v and v <= m then if ar[v] < 0 then ar[v] := n; dec(mc); write((v,n)); end; end; inc(n); end; writeln(); for j := 0 to m do write(ar[j],","); end;
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