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

Author

Amarnath Murthy, Apr 19 2001

Keywords

• nonn
• base

Examples

			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.
		

Links

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

Crossrefs

Cf. A000010, A038566.

Programs

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

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

Extensions

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