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

Author

Antti Karttunen, Dec 08 2015

Keywords

• nonn

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

Crossrefs

Cf. A265388.

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

Programs

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 *)

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