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A067271
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Numbers n such that the digits of P_7(n), the n-th heptagonal number, end in n.
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0
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Recall that P_7(n) = n(5n-3)/2.
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EXAMPLE
| P_7(n) = 188, ending in 8. Hence 8 is a term of the sequence.
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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]] (* From Harvey P. Dale, Jul 12 2011 *)
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CROSSREFS
| Sequence in context: A020668 A020934 A094004 * A064394 A092022 A190200
Adjacent sequences: A067268 A067269 A067270 * A067272 A067273 A067274
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KEYWORD
| base,nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 21 2002
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