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A319355
Filter sequence constructed from the lengths of arithmetic progressions occurring among the divisors of n.
2
1, 2, 2, 3, 2, 4, 2, 5, 3, 5, 2, 6, 2, 5, 4, 7, 2, 8, 2, 9, 5, 5, 2, 10, 3, 5, 5, 11, 2, 12, 2, 9, 5, 5, 5, 13, 2, 5, 5, 14, 2, 15, 2, 9, 16, 5, 2, 17, 3, 9, 5, 9, 2, 18, 5, 15, 5, 5, 2, 19, 2, 5, 9, 20, 5, 18, 2, 9, 5, 21, 2, 22, 2, 5, 8, 9, 5, 15, 2, 23, 7, 5, 2, 24, 5, 5, 5, 21, 2, 25, 4, 9, 5, 5, 5, 26, 2, 9, 9, 27, 2, 15, 2, 21, 28
OFFSET
1,2
COMMENTS
Restricted growth sequence transform of A319354.
For all i, j:
a(i) = a(j) => A067131(i) = A067131(j).
a(i) = a(j) => A160752(i) = A160752(j).
a(i) = a(j) => A091009(i) = A091009(j).
LINKS
PROG
(PARI)
up_to = 65537;
rgs_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), u=1); for(i=1, length(invec), if(mapisdefined(om, invec[i]), my(pp = mapget(om, invec[i])); outvec[i] = outvec[pp] , mapput(om, invec[i], i); outvec[i] = u; u++ )); outvec; };
A319354(n) = if(1==n, 2, my(d=divisors(n), m=1); for(i=1, (#d-1), for(j=(i+1), #d, my(c=1, k=d[j], s=(d[j]-d[i])); while(!(n%k), k+=s; c++); m *= prime(c))); (m));
v319355 = rgs_transform(vector(up_to, n, A319354(n)));
A319355(n) = v319355[n];
CROSSREFS
Cf. A319354.
Sequence in context: A305983 A370816 A305813 * A129294 A363719 A363723
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 21 2018
STATUS
approved