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 A110590 Balanced numbers n (A020492) such that phi(n) is not divisible by 12. 1
 1, 2, 3, 6, 12, 14, 15, 30, 264, 3828 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The only balanced numbers such that sigma(n) is not divisible by 12 are 1, 2, 3. a(11) if it exists is greater than 10^8. - Michel Marcus, Aug 06 2013 a(11) if it exists is greater than 10^13. - Giovanni Resta, Jul 13 2015 LINKS FORMULA n such that sigma(n)/phi(n) is an integer and phi(n) mod 12 != 0. MAPLE with(numtheory): BNM:=[]: for z from 1 to 1 do for n from 1 to 100000 do if phi(n) mod 12 > 0 and sigma(n) mod phi(n) = 0 then BNM:=[op(BNM), n] fi; od; od; BNM; # after 3828 there no others up to 2*10^6. MATHEMATICA fQ[n_] := Block[{ds = DivisorSigma[1, n], ep = EulerPhi@n}, Mod[ep, 12] > 0 && IntegerQ[ds/ep]]; Do[ If[ fQ@n, Print@n], {n, 4*10^8}] (* Robert G. Wilson v, Jun 19 2006 *) CROSSREFS Cf. A000010, A000203, A020492. Sequence in context: A015765 A015771 A020492 * A329401 A291174 A281110 Adjacent sequences:  A110587 A110588 A110589 * A110591 A110592 A110593 KEYWORD nonn,more AUTHOR Walter Kehowski, Sep 13 2005 STATUS approved

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Last modified February 20 22:47 EST 2020. Contains 332086 sequences. (Running on oeis4.)