A138960 - OEIS

A138960

a(n) = smallest prime divisor of A138957(n).

1, 2, 3, 2, 3, 2, 127, 2, 3, 857, 3, 3, 18503, 3, 3, 43, 3, 3, 17, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 7, 3, 3, 1051, 3, 3, 67103, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2

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OFFSET

1,2

COMMENTS

For largest prime divisors see A138961.

LINKS

Table of n, a(n) for n=1..69.

MATHEMATICA

a = {}; b = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[Length[w] - k + 1]]], {k, 1, Length[w]}]; p = FromDigits[a]; AppendTo[b, First[First[FactorInteger[p]]]], {n, 1, 38}]; b

A137957[n_] := FromDigits[Flatten[Reverse /@ IntegerDigits[Range[n]]]];

Table[FactorInteger[A137957[n]][[1, 1]], {n, 39}] (* Robert Price, May 10 2019 *)

CROSSREFS

Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138961.

Sequence in context: A251089 A119880 A075019 * A376545 A245553 A370455

Adjacent sequences: A138957 A138958 A138959 * A138961 A138962 A138963

KEYWORD

nonn,base

AUTHOR

Artur Jasinski, Apr 04 2008

EXTENSIONS

a(39)-a(69) from Robert Price, May 10 2019

STATUS

approved