A178913 a(n) is the number of integer bases r, where r is less than or equal to n, in which n cannot be expressed in the form of k+Reverse(k) for any k

0, 1, 1, 2, 1, 5, 2, 6, 1, 9, 3, 11, 4, 11, 5, 13, 5, 17, 6, 17, 8, 21, 7, 21, 9, 23, 10, 27, 8, 29, 12, 28, 13, 31, 12, 33, 17, 36, 15, 38, 13, 41, 18, 40, 19, 45, 18, 46, 20, 46, 20, 51, 22, 52, 21, 53, 26, 56, 24, 58, 27, 57, 27, 59, 27, 64, 29, 65, 30, 69, 28, 70, 34, 69, 33, 74

Offset

2,4

Links

Table of n, a(n) for n=2..77.

Mathematica

rev[x_, b_] := If[Length[x] < 0, FromDigits[Reverse[IntegerDigits[x, b]], b], Table[FromDigits[Reverse[IntegerDigits[x[[q]], b]], b], {q, 1, Length[x]}]] revadd[x_, b_] := rev[x, b] + x raseeds[max_, b_] := Complement[Range[max], revadd[Range[max], b]] posnumlist[x_] := Transpose[{x, Range[Length[x]]}] posof[x_, y_] := If[Length[x] ==0, Select[Table[If[y[[n]] == x, Last[posnumlist[y][[n]]]], {n, 1, Length[y]}], IntegerQ], Table[ Select[Table[If[y[[n]] == x[[w]], Last[posnumlist[y][[n]]]], {n, 1, Length[y]}], IntegerQ], {w, 1, Length[x]}]] frequ[x_, wer_] := If[Length[x] == 0, Length[posof[x, Flatten[wer]]], Table[ Length[posof[x[[uh]], Flatten[wer]]], {uh, 1, Length[x]}]] Table[frequ[w, Table[raseeds[w, h], {h, 2, w}]], {w, 2, INSERT DESIRED NUMBER OF TERMS HERE}]

Crossrefs

Sequence in context: A087620 A253809 A262213 * A142721 A316891 A152992

Adjacent sequences: A178910 A178911 A178912 * A178914 A178915 A178916

Keyword

base,easy,nonn

Author

Dylan Hamilton, Jun 22 2010

Status

approved