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 A192008 Modified linear pay-phone sequence: number of ways to occupy n pay-phones in a row one-by-one, each time picking a phone adjacent to the smallest number of previously occupied phones. 3
 1, 2, 4, 8, 32, 96, 456, 2016, 11232, 61632, 419328, 2695680, 21358080, 161049600, 1433894400, 12429158400, 123511910400, 1202903654400, 13229501644800, 143113833676800, 1722282128179200, 20516624400384000, 268083853148160000, 3485314242772992000, 49167975665958912000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Max Alekseyev, Table of n, a(n) for n = 1..100 Project Euler, Comfortable distance (Problem 364). Jens Voß, Java class for generating A192008 FORMULA a(n) = SUM (m+k+1)!*binomial(m+k,m)*2^k*(k+v1+v2)!*(m+k)!, where the sum is taken over v1,v2 each from 0 to 1, and over nonnegative m,k such that 2*m+3*k = n-1-v1-v2. - Max Alekseyev, Sep 11 2016 EXAMPLE For n=4, the A192008(n) = 8 ways of picking the phones are (1, 3, 4, 2), (1, 4, 2, 3), (1, 4, 3, 2), (2, 4, 1, 3), (3, 1, 4, 2), (4, 1, 2, 3), (4, 1, 3, 2), (4, 2, 1, 3). PROG (PARI) { A192008(n) = my(r, k); r=0; for(v=0, 2, forstep(m=lift(Mod(n-1-v, 3)/2), (n-1-v)\2, 3, k=(n-1-v-2*m)\3; r+=(m+k+1)!*binomial(m+k, m)*2^k*(k+v)!*(m+k)!*(1+(v==1)); ); ); r; } \\ Max Alekseyev, Sep 11 2016 CROSSREFS Cf. A095236, A192009, A276657. Sequence in context: A271216 A102000 A165904 * A298989 A074406 A186340 Adjacent sequences:  A192005 A192006 A192007 * A192009 A192010 A192011 KEYWORD nonn AUTHOR Jens Voß, Jun 21 2011 EXTENSIONS More terms from João Batista Souza de Oliveira, Jul 09 2014 Terms a(20) onward from Max Alekseyev, Sep 11 2016 STATUS approved

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Last modified November 21 12:23 EST 2018. Contains 317449 sequences. (Running on oeis4.)