A138962 a(1) = 1, a(n) = the smallest prime divisor of A138793(n).

1, 3, 3, 29, 3, 3, 19, 3, 3, 457, 3, 3, 16087, 3, 3, 35963, 3, 3, 167, 3, 3, 7, 3, 3, 13, 3, 3, 953, 3, 3, 7, 3, 3, 548636579, 3, 3, 19, 3, 3, 71, 3, 3, 13, 3, 3, 89, 3, 3, 114689, 3, 3, 17, 3, 3, 12037, 3, 3, 7, 3, 3

Offset

1,2

Comments

a(61) > 10^11. - Robert Price, Mar 22 2015

Links

Daniel Suteu, Table of n, a(n) for n = 1..333

Formula

a(n) = A020639(A138793(n)). - Daniel Suteu, May 27 2022

Mathematica

b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; AppendTo[b, First[First[FactorInteger[p]]]], {n, 1, 31}]; b (* Artur Jasinski, Apr 04 2008 *)
lst = {}; Table[First[First[FactorInteger[FromDigits[Reverse[lst = Join[lst, IntegerDigits[n]]]]]]], {n, 1, 60}] (* Robert Price, Mar 22 2015 *)

Prog

(PARI)
f(n) = my(D = Vec(concat(apply(s->Str(s), [1..n])))); eval(concat(vector(#D, k, D[#D-k+1]))); \\ A138793
a(n) = my(k=f(n)); forprime(p=2, 10^6, if(k%p == 0, return(p))); if(n == 1, 1, vecmin(factor(k)[, 1])); \\ Daniel Suteu, May 27 2022

Crossrefs

Cf. A020639, A138793, A104759, A000422, A116504, A007908, A116505, A104759, A075019, A075020, A075021, A075022, A138789, A138790, A138960, A138962.

Sequence in context: A098340 A271938 A075020 * A139206 A100651 A124244

Adjacent sequences: A138959 A138960 A138961 * A138963 A138964 A138965

Keyword

nonn

Author

Artur Jasinski, Apr 04 2008

Extensions

a(32)-a(60) from Robert Price, Mar 22 2015

Status

approved