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A113940
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Triangular numbers that are also brilliant (A078972).
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2
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6, 10, 15, 21, 253, 703, 1081, 1711, 1891, 2701, 3403, 25651, 34453, 38503, 49141, 60031, 64261, 73153, 79003, 88831, 104653, 108811, 114481, 126253, 146611, 158203, 171991, 188191, 218791, 226801, 258121, 269011, 286903, 351541
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Smallest value where each factor has n digits for n = 1, 2, 3, 4, 5, are: 6 = 2 * 3; 253 = 11 * 23; 25651 = 113 * 227; 2035153 = 1009 * 2017; 202457503 = 10061 * 20123. [From Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 04 2009]
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FORMULA
| A000217 INTERSECTION A078972. Subset of A068443. [From Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 04 2009]
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EXAMPLE
| 253=T(22) and 253=11*23 is brilliant.
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MATHEMATICA
| brilQ[n_]:=Module[{fin=FactorInteger[n]}, Total[Transpose[fin][[2]]]==2&& Length[Union[IntegerLength[Transpose[fin][[1]]]]]==1]
Intersection[Accumulate[Range[850]], Select[Range[362000], brilQ]] (* From Harvey P. Dale, Feb 06 2011 *)
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CROSSREFS
| Cf. A068443, A078972.
Cf. A000217. [From Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 04 2009]
Sequence in context: A122783 A124000 A068443 * A099981 A022949 A049694
Adjacent sequences: A113937 A113938 A113939 * A113941 A113942 A113943
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KEYWORD
| base,nonn
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AUTHOR
| Giovanni Resta (g.resta(AT)iit.cnr.it), Jan 31 2006
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