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Search: id:A116993
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| A116993 |
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a(n) is the least number having exactly n representations as a product of two palindromes. |
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+0
3
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| 13, 1, 4, 44, 66, 484, 4444, 7326, 6666, 48884, 73326, 493284, 888888, 666666, 5426124, 4888884, 6672666, 7333326, 44888844
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OFFSET
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0,1
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COMMENT
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a(20) <= 733333326; a(34) <= 666666666666; a(39) <= 4888888888884 and a(44) <= 7333333333326. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 10 2006
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EXAMPLE
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a(0)=13 since 13 is the smallest number that cannot be represented as a product of two palindromes. a(5)=484 since 484= 1*484 = 2*242 = 4*121 = 22*22 = 11*44.
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MATHEMATICA
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f[n_]:=f[n]=Length[Select[Divisors[n], #<=n^(1/2)&&FromDigits[ Reverse[IntegerDigits[ # ]]]==#&&FromDigits[Reverse[IntegerDigits [n/# ]]]==n/#&]]; a[n_]:=(For[m=1, f[m] != n, m++ ]; m); Do[Print[a[n]], {n, 0, 18}] - Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 10 2006
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CROSSREFS
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Cf. A002113, A125832, A125833, A125834.
Adjacent sequences: A116990 A116991 A116992 this_sequence A116994 A116995 A116996
Sequence in context: A089568 A010232 A010233 this_sequence A010234 A111738 A010235
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KEYWORD
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base,nonn
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AUTHOR
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Giovanni Resta (g.resta(AT)iit.cnr.it), Apr 02 2006
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EXTENSIONS
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More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 10 2006
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