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Search: id:A074837
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| A074837 |
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Numbers n such that the penultimate 3 divisors of n sum to n. |
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+0
1
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| 6, 18, 42, 54, 66, 78, 102, 114, 126, 138, 162, 174, 186, 198, 222, 234, 246, 258, 282, 294, 306, 318, 342, 354, 366, 378, 402, 414, 426, 438, 462, 474, 486, 498, 522, 534, 546, 558, 582, 594, 606, 618, 642, 654, 666, 678, 702, 714, 726, 738, 762, 774, 786
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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It seems that only numbers that are 6 mod 12 are present except for multiples of 30.
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EXAMPLE
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18 has the divisors 1,2,3,6,9,18. The penultimate 3 are 3,6,9, which sum to 18.
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MATHEMATICA
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Select[Range[1000], Length[Divisors[ # ]]>3 && Sum[Divisors[ # ][[ -i]], {i, 2, 4}]==# &] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Aug 01 2007
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PROGRAM
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(PARI) for (n=1, 300, dn=divisors(n); dnl=length(dn); if (dnl>3, if (n==dn[dnl-1]+dn[dnl-2]+dn[dnl-3], print(n))))
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CROSSREFS
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Sequence in context: A015224 A163983 A023620 this_sequence A015942 A009945 A011930
Adjacent sequences: A074834 A074835 A074836 this_sequence A074838 A074839 A074840
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KEYWORD
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nonn
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AUTHOR
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Jon Perry (perry(AT)globalnet.co.uk), Sep 09 2002
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Aug 01 2007
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