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 A164904 a(n) is the number of palindromic structures using a maximum of ten different symbols. 3
 1, 1, 1, 2, 2, 5, 5, 15, 15, 52, 52, 203, 203, 877, 877, 4140, 4140, 21147, 21147, 115975, 115975, 678569, 678569, 4213530, 4213530, 27641927, 27641927, 190829797, 190829797, 1381367941, 1381367941, 10448276360, 10448276360, 82285618467 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS a(n) is the number of palindromic word structures of length n using 10-ary alphabet. a(n) is the same as taking every element twice from A164864 - Number of ways of placing n labeled balls into 10 indistinguishable boxes; word structures of length n using a 10-ary alphabet. LINKS Index entries for linear recurrences with constant coefficients, signature (1, 45, -45, -861, 861, 9135, -9135, -58674, 58674, 233100, -233100, -557864, 557864, 732960, -732960, -403200, 403200). FORMULA G.f.: (148329*x^17 -403200*x^16 -210253*x^15 +732960*x^14 +122692*x^13 -557864*x^12 -38365*x^11 +233100*x^10 +6965*x^9 -58674*x^8 -736*x^7 +9135*x^6 +42*x^5 -861*x^4 -x^3 +45*x^2 -1) / ((x -1)*(2*x -1)*(2*x +1)*(2*x^2 -1)*(3*x^2 -1)*(5*x^2 -1)*(6*x^2 -1)*(7*x^2 -1)*(8*x^2 -1)*(10*x^2 -1)). [Colin Barker, Dec 05 2012] EXAMPLE Four-digit palindromes have two different digits structures: aaaa and abba. Hence a(4)=2. CROSSREFS Cf. A056470, A056471, A164864, A188164 Sequence in context: A055879 A056470 A056471 * A188164 A245846 A245847 Adjacent sequences:  A164901 A164902 A164903 * A164905 A164906 A164907 KEYWORD nonn,easy AUTHOR Tanya Khovanova, Aug 30 2009 STATUS approved

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Last modified December 5 03:59 EST 2021. Contains 349530 sequences. (Running on oeis4.)