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Index of smallest triangular number beginning with the n-th triangular number other than itself.

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`%I #4 Mar 13 2015 00:57:25
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`%S 4,8,11,14,17,20,75,85,95,105,36,39,135,145,155,165,553,58,616,648,
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`%T 680,711,743,77,806,838,869,901,933,96,996,1028,1059,1091,1122,1154,
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`%U 1186,1217,1249,4050,1312,1344,1375,1407,4550,1470,1502,4850,1565,5050
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`%N Index of smallest triangular number beginning with the n-th triangular number other than itself.
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`%e a(7) = 75 as the 75th triangular number 2850 > 28 is the smallest triangular number beginning with 28 which is the seventh triangular number.
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`%Y Cf. A072517.
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`%K base,nonn
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`%O 1,1
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`%A _Amarnath Murthy_, Jul 31 2002
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`%E Corrected and extended by Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 25 2003
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