A067271 - OEIS

A067271

Numbers n such that the digits of P_7(n), the n-th heptagonal number, end in n.

1, 4, 5, 8, 9, 16, 25, 40, 41, 56, 65, 80, 81, 96, 176, 225, 400, 401, 576, 625, 800, 801, 976, 1376, 2625, 4000, 4001, 5376, 6625, 8000, 8001, 9376, 10625, 29376, 40000, 40001, 50625, 69376, 80000, 80001, 90625

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OFFSET

1,2

COMMENTS

Recall that P_7(n) = n(5n-3)/2.

LINKS

Table of n, a(n) for n=1..41.

EXAMPLE

P_7(n) = 188, ending in 8. Hence 8 is a term of the sequence.

MATHEMATICA

(*returns true if a ends with b, false o.w.*) f[a_, b_] := Module[{c, d, e, g, h, i, r}, r = False; c = ToString[a]; d = ToString[b]; e = StringLength[c]; g = StringPosition[c, d]; h = Length[g]; If[h > 0, i = g[[h]]; If[i[[2]] == e, r = True]]; r]; Do[If[f[n(5n-3)/2, n], Print[n]], {n, 1, 10^5} ]

Transpose[Select[Table[{n, n (5n-3)/2}, {n, 100000}], Mod[Last[#], 10^IntegerLength[ First[#]]]==First[#]&]][[1]] (* Harvey P. Dale, Jul 12 2011 *)

CROSSREFS

Sequence in context: A020934 A094004 A228012 * A268128 A064394 A346457

Adjacent sequences: A067268 A067269 A067270 * A067272 A067273 A067274

KEYWORD

base,nonn

AUTHOR

Joseph L. Pe, Feb 21 2002

STATUS

approved