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 A061097 a(n) is the concatenation of the phi(n) numbers between 1 and n that are relatively prime to n. 1
 1, 1, 12, 13, 1234, 15, 123456, 1357, 124578, 1379, 12345678910, 15711, 123456789101112, 13591113, 12478111314, 13579111315, 12345678910111213141516, 157111317, 123456789101112131415161718 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified January 29 04:57 EST 2020. Contains 331335 sequences. (Running on oeis4.)