A130172 Let f(i) = prime( f(i - 1) (modulo 10^n) ) with f(0) = 1; a(n) is the term where the period of the sequence f(i) begins to repeat.

2, 4, 2, 62, 221, 301, 1062, 860, 21189, 35835, 116119, 317168, 3000313

Offset

1,1

Links

Table of n, a(n) for n=1..13.

Example

For a(1), the sequence is 1, 2, 3, 5, 11, 2, 3, 5, 11, 2, 3,
5, 11, ... The sequence has period {2, 3, 5, 11} so a(1) = 2.
For a(2) see the A112279: 1, 2, 3, 5, 11, 31, 127, 103, 5,
11, 31, 127, 103, 5, 11, ..., . This sequence has a cyclic length of 5,
the terms {5, 11, 31, 127, 103} and the first term 5 first appears at
the fourth term.

Mathematica

f[n_] := Block[{k = 1, a}, a[0] = 1; a[i_] := a[i] = Prime[Mod[a[i - 1], 10^n]]; While[t = Table[a[i], {i, 0, k - 1}]; MemberQ[t, a[k]] == False, k++ ]; Flatten[ Position[t, a[k]]][[1]]]; Array[ f, 8]

Crossrefs

Cf. A128867.

Sequence in context: A263931 A259685 A301460 * A303320 A029589 A121819

Adjacent sequences: A130169 A130170 A130171 * A130173 A130174 A130175

Keyword

nonn,more

Author

Robert G. Wilson v, May 13 2007

Extensions

a(9)-a(11) from Chai Wah Wu, Sep 26 2019

a(12)-a(13) from Chai Wah Wu, Oct 02 2019

Status

approved