A069896 GCD of consecutive values of Chowla's function.

0, 0, 2, 2, 5, 5, 6, 3, 1, 7, 15, 15, 9, 1, 2, 14, 20, 20, 21, 1, 1, 13, 35, 5, 5, 3, 3, 27, 41, 41, 30, 2, 1, 1, 6, 54, 21, 1, 1, 49, 53, 53, 39, 1, 1, 25, 75, 1, 7, 2, 5, 45, 65, 1, 1, 1, 1, 31, 107, 107, 33, 1, 2, 2, 1, 77, 57, 1, 1, 73, 122, 122, 39, 3, 3, 9, 1, 89, 105, 3, 1, 43

Offset: 1

Author

Labos Elemer, Apr 10 2002

Keywords

• easy
• nonn

Examples

			Chowla's function values from 92 to 96 are 75,34,49,24,155: successive values are relatively primes.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A048050, A000203, A001650.

Programs

Mathematica

m = 100; s = Array[If[# == 1, 0, DivisorSigma[1, #] - # - 1] &, {m}]; GCD[s[[1 ;; m - 1]], s[[2 ;; m]]] (* Amiram Eldar, Aug 28 2019 *)

Formula

a(n) = gcd(sigma(n+1)-(n+1)-1, sigma(n)-n-1), for n > 1.

Extensions

a(1) corrected by Amiram Eldar, Aug 28 2019