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0, 7, 26, 63, 124, 215, 342, 511, 728, 999, 1330, 1727, 2196, 2743, 3374, 4095, 4912, 5831, 6858, 7999, 9260, 10647, 12166, 13823, 15624, 17575, 19682, 21951, 24388, 26999, 29790, 32767, 35936, 39303, 42874, 46655, 50652, 54871, 59318, 63999
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(n) is the least positive integer k such that k can only contain 'n-1' in exactly 2 different bases B, where 1<B<=k.
A129294(n) = number of divisors of a(n) that are not greater than n. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 09 2007
Apart from the first term, the same as A135300. R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 29 2008
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LINKS
| Nathaniel Johnston, Table of n, a(n) for n = 1..10000
Index to sequences with linear recurrences with constant coefficients, signature (4,-6,4,-1).
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FORMULA
| Partial sums of A003215, hex (or centered hexagonal) numbers: 3n(n+1)+1. - Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 16 2006
G.f.: x^2*(7-2*x+x^2)/(1-x)^4. [Colin Barker, Feb 12 2012]
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EXAMPLE
| For n=6; 215 written in bases 6 and 42 is 555, 55 and (555, 55) are exactly 2 different bases.
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MATHEMATICA
| f[n_]:=n^3-1; f[Range[60]] (*From Vladimir Joseph Stephan Orlovsky, Feb 14 2011*)
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PROG
| (PARI) a(n)=n^3-1
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CROSSREFS
| Cf. A000217, A005448, A016921.
Sequence in context: A128972 A135300 A024001 * A006325 A053346 A180669
Adjacent sequences: A068598 A068599 A068600 * A068602 A068603 A068604
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KEYWORD
| easy,nonn,changed
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AUTHOR
| Naohiro Nomoto (n_nomoto(AT)yabumi.com), Mar 28 2002
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