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Search: id:A117709
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| A117709 |
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Pentagonal numbers for which the sum of the digits is also a pentagonal number. |
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+0
1
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| 0, 1, 5, 651, 1335, 2262, 3432, 3577, 6501, 8400, 8626, 10542, 10795, 15862, 18760, 21540, 25285, 28912, 32340, 32782, 45850, 50142, 50692, 55200, 60501, 72490, 91390, 98945, 104412, 112477, 127750, 135751, 152482, 160230, 170185, 179401
(list; graph; listen)
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OFFSET
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0,3
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EXAMPLE
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651 is in the sequence because it is a pentagonal number and the sum of its digits 6+5+1=12 is also a pentagonal number.
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MAPLE
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a:=proc(n) local P, s: P:=convert(n*(3*n-1)/2, base, 10): s:=add(P[j], j=1..nops(P)): if n=0 then 0 elif type((1+sqrt(1+24*s))/6, integer)=true then n*(3*n-1)/2 else fi end: seq(a(n), n=0..350); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 15 2006
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CROSSREFS
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Cf. A000326.
Sequence in context: A060758 A068421 A142535 this_sequence A133750 A090947 A000367
Adjacent sequences: A117706 A117707 A117708 this_sequence A117710 A117711 A117712
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KEYWORD
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base,nonn
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), Apr 13 2006
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