A061097 a(n) is the concatenation of the phi(n) numbers between 1 and n that are relatively prime to n.

1, 1, 12, 13, 1234, 15, 123456, 1357, 124578, 1379, 12345678910, 15711, 123456789101112, 13591113, 12478111314, 13579111315, 12345678910111213141516, 157111317, 123456789101112131415161718

Offset

1,3

Links

Robert Israel, Table of n, a(n) for n = 1..372

Example

a(6) = 15, 1 and 5 are the two coprime numbers less than 6.
a(7) = 123456. 7 is a prime. phi(7) = 6 hence all the numbers less than 7 are concatenated.

Maple

f:= proc(n) local i, t;
  t:= 1;
  for i from 2 to n-1 do if igcd(i, n)=1 then t:= t*10^(1+ilog10(i))+i fi od;
  t
end proc:
map(f, [$1..30]); # Robert Israel, Jun 13 2018

Prog

(PARI) a(n)=j=0; for(k=1, n, if(gcd(k, n)==1, j=j*10^#digits(k)+k)); j \\ Eric Chen, Jun 13 2018
(PARI) a(n) = eval(concat(apply(x->Str(x), select(x->(gcd(n, x) == 1), [1..n])))); \\ Michel Marcus, Jun 14 2018

Crossrefs

Cf. A000010, A038566.

Sequence in context: A066321 A099415 A042293 * A121288 A075477 A075482

Adjacent sequences: A061094 A061095 A061096 * A061098 A061099 A061100

Keyword

nonn,base

Author

Amarnath Murthy, Apr 19 2001

Extensions

a(11)-a(19) from Carl Najafi, Apr 30 2011

Status

approved