A265394 Positions of records in A265388.

1, 2, 3, 6, 7, 15, 19, 31, 37, 79, 97, 139, 157, 199, 211, 229, 271, 307, 331, 337, 367, 379, 439, 499, 547, 577, 601, 607, 619, 661, 691, 727, 811, 829, 877, 937, 967, 997, 1009, 1069, 1171, 1237, 1279, 1297, 1399, 1429, 1459, 1531, 1609, 1627, 1657, 1759, 1867, 2011, 2029, 2089, 2131, 2137, 2179, 2221, 2281, 2311

Offset

1,2

Comments

Question: Apart from a(1)=1, a(4)=6 and a(6)=15, are all other terms primes? See also comments in A265395 & A265396.

Links

Antti Karttunen, Table of n, a(n) for n = 1..192

Mathematica

DeleteDuplicates[Table[{n, GCD@@Array[Binomial[2 n, 2 #]&, {n-1}]}, {n, 2350}], GreaterEqual[ #1[[2]], #2[[2]]]&][[All, 1]] (* Harvey P. Dale, Jul 19 2022 *)

Prog

(PARI) lista(nn) = {r = 0; for (n=1, nn, nr = gcd(vector(n-1, k, binomial(2*n, 2*k))); if (nr > r, print1(n, ", "); r = nr); ); } \\ Michel Marcus, Dec 08 2015

Crossrefs

Cf. A265388.

Cf. A265395 (gives the record values), A265396.

Sequence in context: A245479 A294524 A032882 * A125167 A137604 A034901

Adjacent sequences: A265391 A265392 A265393 * A265395 A265396 A265397

Keyword

nonn

Author

Antti Karttunen, Dec 08 2015

Status

approved