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 A137740 Number of different strings of length n+5 obtained from "123...n" by iteratively duplicating any substring. 12
 1, 32, 138, 348, 700, 1246, 2050, 3188, 4749, 6836, 9567, 13076, 17514, 23050, 29872, 38188, 48227, 60240, 74501, 91308, 110984, 133878, 160366, 190852, 225769, 265580, 310779, 361892, 419478, 484130, 556476, 637180, 726943, 826504, 936641, 1058172, 1191956 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS See A137743 for comments and examples. LINKS Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1). FORMULA a(n) = (n+4)(n^2+3n-8)(n^2+23n+150)/5!+4 for n>4. G.f.: x*(x^8+2*x^7-7*x^6-20*x^5+57*x^4-20*x^3-39*x^2+26*x+1) / (x-1)^6. - Colin Barker, Nov 04 2013 PROG (PARI) A137740(n)=if(n<2, 1, n=A135473(n+5, n); n[ #n]) /* function A135473 defined in A137743 */ (PARI) A137740(n)=if(n>4, n*(n*(n*(n*(n+30)+315)+1110)-136)/5!-36, [1, 32, 138, 348][n]) CROSSREFS Cf. A137739-A137743, A135473, A137744-A137748. Sequence in context: A299386 A299185 A299946 * A221597 A159763 A100164 Adjacent sequences:  A137737 A137738 A137739 * A137741 A137742 A137743 KEYWORD nonn,easy AUTHOR M. F. Hasler, Feb 10 2008 EXTENSIONS More terms from Colin Barker, Nov 04 2013 STATUS approved

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Last modified December 12 17:01 EST 2018. Contains 318078 sequences. (Running on oeis4.)