A084315 - OEIS

A084315

a(n) = x is the smallest number such that gcd(prime(x)-1,x-1) = n.

1, 3, 4, 13, 36, 19, 120, 33, 46, 11, 78, 37, 560, 239, 496, 1905, 52, 397, 3250, 221, 778, 573, 2738, 25, 26, 287, 352, 477, 552, 271, 8588, 449, 5710, 205, 456, 145, 1000, 4067, 2536, 761, 14638, 295, 4344, 2685, 406, 1151, 612, 3121, 6616, 551, 868, 469, 20088

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OFFSET

1,2

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..4000

FORMULA

a(n) = Min{x; A084311(x)=n}.

EXAMPLE

In A084311, n=4 arises first at the 13th position, so a(4)=13.

MATHEMATICA

f[x_] := GCD[Prime[x]-1, x-1] t=Table[0, {256}]; Do[s=f[n]; If[s<257&&t[[s]]==0, t[[s]]=n], {n, 1, 100000}]; t

CROSSREFS