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 A116993 a(n) is the least number having exactly n representations as a product of two palindromes. 2
 13, 1, 4, 44, 66, 484, 4444, 7326, 6666, 48884, 73326, 493284, 888888, 666666, 5426124, 4888884, 6672666, 7333326, 44888844, 73399326, 246888642, 67333266, 4073662593, 4893772884, 4533773244, 6800659866, 2715775062, 1481331852 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(20) <= 733333326; a(34) <= 666666666666; a(39) <= 4888888888884 and a(44) <= 7333333333326. - Farideh Firoozbakht, Dec 10 2006 LINKS Table of n, a(n) for n=0..27. EXAMPLE 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. MATHEMATICA 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, Dec 10 2006 CROSSREFS Cf. A002113, A125832, A125833, A125834. Sequence in context: A010232 A010233 A159820 * A010234 A111738 A202134 Adjacent sequences: A116990 A116991 A116992 * A116994 A116995 A116996 KEYWORD base,nonn AUTHOR Giovanni Resta, Apr 02 2006 EXTENSIONS More terms from Farideh Firoozbakht, Dec 10 2006 a(19)-a(27) from Donovan Johnson, Aug 04 2009 STATUS approved

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Last modified June 22 22:13 EDT 2024. Contains 373619 sequences. (Running on oeis4.)