OFFSET
1,2
COMMENTS
If there is any number present which itself is not divisible by 3 (is in A001651), then 3n is also present in this sequence.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
PROG
(PARI)
\\ A naivish algorithm:
allocatemem(2^30);
up_to_level = 10;
up_to = (3^(1+up_to_level))-1;
vekkuli = vector(up_to);
vekkuli[1] = 1;
vekkuli[2] = -1;
write("b293523.txt", 1, " ", 1);
write("b293523.txt", 2, " ", 2);
kA293523 = 3; for(n=3, up_to, vekkuli[n] = moebius(n)*vekkuli[n\3]; if(vekkuli[n], write("b293523.txt", kA293523, " ", n); kA293523++; ));
(PARI)
is_persistently_squarefree(n, base) = { while(n>1, if(!issquarefree(n), return(0)); n \= base); (1); };
isA293523(n) = is_persistently_squarefree(n, 3);
n=0; k=1; while(k <= 10000, n=n+1; if(isA293523(n), write("b293523.txt", k, " ", n); k=k+1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Oct 11 2017
STATUS
approved