A079792 a(1) = 1, a(n) = a(n-1)/gcd(a(n-1),n) if gcd(a(n-1),n) > 1 otherwise a(n) is the concatenation of a(n-1) and n.

1, 12, 4, 1, 15, 5, 57, 578, 5789, 578910, 57891011, 5789101112, 578910111213, 82701444459, 27567148153, 2756714815316, 275671481531617, 27567148153161718, 2756714815316171819, 275671481531617181920, 39381640218802454560, 19690820109401227280, 1969082010940122728023

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..394

Example

a(3) = 12/3 = 4, a(4) = 4/4 = 1, a(5) = 15, a(6) = 15/3 = 5.

Maple

tcat:= proc(a, b) a*10^(1+ilog10(b))+b end proc:
A[1]:= 1:
for n from 2 to 100 do
  g:= igcd(A[n-1], n);
  if g >1 then A[n]:= A[n-1]/g else A[n]:= tcat(A[n-1], n) fi;
od:
convert(A, list); # Robert Israel, Dec 03 2024

Mathematica

a[1] = 1; a[n_] := a[n] = Block[{b = GCD[a[n - 1], n]}, If[b > 1, a[n - 1]/b, FromDigits[ Join[ IntegerDigits[ a[n - 1]], IntegerDigits[ n]]]]]; Table[a[n], {n, 1, 20}]

Crossrefs

Cf. A079791.

Sequence in context: A098909 A261403 A010202 * A079791 A018812 A306375

Adjacent sequences: A079789 A079790 A079791 * A079793 A079794 A079795

Keyword

base,nonn

Author

Amarnath Murthy, Feb 04 2003

Extensions

Edited and extended by Robert G. Wilson v, Feb 04 2003

Status

approved