A240978 The largest prime divisor of A246053(n).

2, 2, 7, 31, 127, 73, 691, 8191, 3617, 131071, 524287, 593, 2294797, 657931, 362903, 1001259881, 2147483647, 151628697551, 26315271553053477373, 154210205991661, 1897170067619, 1520097643918070802691, 1798482437, 67568238839737, 153289748932447906241

Offset

0,1

Comments

According to theorem 2 of the Milnor paper a(2) and a(4) through a(8) are lower bounds for the number of distinct differentiable structures on spheres S^(4*k-1) for k = 2 and 4,..,8. Better bounds are given in A242032.

Links

Table of n, a(n) for n=0..24.

John Milnor, Differentiable Structures on Spheres, American Journal of Mathematics, Vol. 81, No. 4 (Oct., 1959), pp. 962-972. [See p. 971]

Formula

a(n) = A006530(A246053(n)). - Michel Marcus, Aug 18 2014

Prog

(Sage)
h = lambda x: zeta(2*x)*(4^x-2)
A246053 = lambda n: Integer((h((n+1)//2)*h(n//2)/h(n)).denominator())
A240978 = lambda n: max(prime_divisors(A246053(n)))
[A240978(n) for n in range(25)]

Crossrefs

Cf. A246053, A246052, A242032.

Sequence in context: A359582 A047003 A067352 * A242032 A350019 A298440

Adjacent sequences: A240975 A240976 A240977 * A240979 A240980 A240981

Keyword

nonn

Author

Peter Luschny, Aug 12 2014

Status

approved