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Search: id:A117661
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| A117661 |
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Heptagonal numbers for which the product of the digits is also a heptagonal number. |
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+0
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| 0, 1, 7, 1782, 9211, 13213, 212722, 252333, 371911, 766459, 3829753, 5743366, 6534297, 6566671, 13336785, 15347493, 15973168, 17831596, 17965381, 19567813, 27335662, 33154947, 37494513, 47539261, 51817693, 78335613, 93657421
(list; graph; listen)
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OFFSET
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1,3
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EXAMPLE
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766459 is in the sequence because it is a heptagonal number and the product of its digits (45360) is also a heptagonal number
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MAPLE
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a:=proc(n) local hn, hnn: hn:=convert(n*(5*n-3)/2, base, 10): hnn:=product(hn[j], j=1..nops(hn)): if type((3+sqrt(9+40*hnn))/10, integer)=true then n*(5*n-3)/2 else fi end: seq(a(n), n=0..10000); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 16 2006
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CROSSREFS
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Cf. A000566.
Sequence in context: A125537 A001424 A055318 this_sequence A145253 A024099 A056235
Adjacent sequences: A117658 A117659 A117660 this_sequence A117662 A117663 A117664
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KEYWORD
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nonn,base
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), Apr 11 2006
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 16 2006
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