A067275 - OEIS

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A067275

Numbers n such that the digits of P_5(n), the n-th pentagonal number, begin with n.

1, 7, 67, 667, 6667, 66667, 666667 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Recall that P(n) = n(3n-1)/2. From the fifth term on, it appears that all terms of the sequence begin with "666". :-)`
	EXAMPLE	`P_5(67) = 6700, beginning in 67. Hence 67 is a term of the sequence.`
	MATHEMATICA	`(returns true if a begins with b, false o.w.) f[a_, b_] := Module[{c, d, e, g, h, i, r}, r = False; c = ToString[a]; d = ToString[b]; g = StringPosition[c, d]; h = Length[g]; If[h > 0, i = g[[h]]; If[i[[1]] == 1, r = True]]; r]; Do[If[f[n(3n - 1)/2, n], Print[n]], {n, 1, 10^6} ]`
	CROSSREFS	`Sequence in context: A077789 A186655 A124291 * A073552 A036948 A020469` `Adjacent sequences: A067272 A067273 A067274 * A067276 A067277 A067278`
	KEYWORD	`base,nonn`
	AUTHOR	`Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 21 2002`

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Last modified February 15 10:28 EST 2012. Contains 205763 sequences.