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A285079
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Oblong numbers the product of whose digits are positive oblong numbers.
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1
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2, 6, 12, 56, 132, 156, 756, 2756, 4556, 6162, 6972, 7656, 13572, 21756, 31152, 33672, 45156, 61752, 84972, 153272, 166872, 279312, 467172, 626472, 661782, 1273512, 1412532, 1541322, 1568756, 1596432, 1786232, 1867322, 2678132, 2817362, 3416952, 3521252
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OFFSET
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1,1
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COMMENTS
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Oblong numbers are numbers of the form k*(k+1) (A002378).
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LINKS
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Robert Israel and Giovanni Resta, Table of n, a(n) for n = 1..391 (terms < 10^25, first 221 terms from Robert Israel)
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MAPLE
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filter:= proc(x) local t; t:= convert(convert(x, base, 10), `*`);
t > 0 and issqr(1+4*t); end proc:
select(filter, [seq(x*(1+x), x=1..10^4)]); # Robert Israel, Apr 14 2017
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MATHEMATICA
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f[x_] := Sqrt[1 + 4 (Times @@ IntegerDigits[x])]; Select[Table[n (n + 1), {n, 1, 10000}], f[#] > 1 && Mod[f[#], 2] == 1 &]
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CROSSREFS
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Cf. A002378, A053059, A069077.
Sequence in context: A152873 A175810 A083001 * A119862 A111936 A232090
Adjacent sequences: A285076 A285077 A285078 * A285080 A285081 A285082
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KEYWORD
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nonn,base
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AUTHOR
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Melvin Peralta, Apr 09 2017
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STATUS
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approved
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