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A335902
Composite numbers c such that phi(c)/phi(mind(c)) mod phi(c)/phi(maxd(c)) <> 0, where phi is the Euler function, mind(c) is the smallest nontrivial divisor of c, maxd(c) is the largest nontrivial divisor of c.
3
35, 55, 77, 95, 115, 119, 143, 155, 161, 187, 203, 209, 215, 221, 235, 245, 247, 253, 287, 295, 299, 319, 323, 329, 335, 355, 371, 377, 391, 395, 403, 407, 413, 415, 437, 473, 493, 497, 515, 517, 527, 533, 535, 551, 559, 581, 583, 589, 605, 611, 623, 629, 635, 649
OFFSET
1,1
COMMENTS
This equivalence criterion splits a set of composite numbers into two classes and can be used to count certain combinatorial objects.
PROG
(MATLAB)
n=500; % gives all terms of the sequence not exceeding n
A=[];
for i=1:n
dn=divisors(i);
if size(dn, 2)>2 && mod (totient(i)/totient(dn(2)), totient(i)/totient(dn(end-1)))~=0
A=[A i];
end
end
function [res] = totient(n)
res=0;
for i=1:n
if gcd(i, n)==1
res=res+1;
end
end
end
(PARI) isok(c) = if ((c>1) && !isprime(c), my(t=eulerphi(c), d=divisors(c)); ((t/eulerphi(d[2])) % (t/eulerphi(d[#d-1]))) != 0); \\ Michel Marcus, Dec 28 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Maxim Karimov, Dec 28 2020
STATUS
approved