This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
Table[GCD @@ Array[Binomial[2 n, 2 #] &, {n - 1}], {n, 1, 66}] (* Michael De Vlieger, Dec 09 2015, modified to match the new corrected data by Antti Karttunen, Dec 11 2015 *)
allocatemem(2^30); A265388(n) = if(n<=1, 0, gcd(vector(n-1, k, binomial(2*n, 2*k)))) \\ PARI versions before 2.8 return an erroneous value 1 for gcd of an empty vector/set. - Michel Marcus, Dec 08 2015 and Antti Karttunen, Dec 11 2015 for(n=1, 10000, write("b265388.txt", n, " ", A265388(n)));
(define (A265388 n) (let loop ((z 0) (k 1)) (cond ((>= k n) z) ((= 1 z) z) (else (loop (gcd z (A007318tr (* 2 n) (* 2 k))) (+ k 1)))))) ;; A version using fold. Instead of fold-left we could as well use fold-right: (define (A265388 n) (fold-left gcd 0 (map (lambda (k) (A007318tr (* 2 n) (* 2 k))) (range1-n (- n 1))))) (define (range1-n n) (let loop ((n n) (result (list))) (cond ((zero? n) result) (else (loop (- n 1) (cons n result)))))) ;; In above code A007318tr(n,k) computes the binomial coefficient C(n,k), i.e., Pascal's triangle A007318. - Antti Karttunen, Dec 11 2015
lista(nn) = {r = 0; for (n=1, nn, nr = gcd(vector(n-1, k, binomial(2*n, 2*k))); if (nr > r, print1(nr, ", "); r = nr););} \\ Michel Marcus, Dec 08 2015. Note: this gives correct value for a(1) only from PARI version 2.8 onward, see A265388 for why. - Antti Karttunen, Dec 11 2015
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