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 A088830 a(n) = Min{x : sigma(x) = n*phi(x), x is not a prime}, the least nonprime solutions to sigma(x) = n*phi(x); special balanced numbers. 6
 1, 35, 15, 14, 56, 6, 12, 42, 30, 168, 2580, 210, 630, 420, 840, 20790, 416640, 9240, 291060, 83160, 120120, 5165160, 1719277560, 43825320, 26860680, 277560360, 1304863560, 569729160, 587133466920, 16522145640, 33044291280, 563462139240, 1140028049160 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(33) > 10^12. - Donovan Johnson, Sep 03 2013 a(34) <= 9015394227840, a(35) <= 1255683068640. - Giovanni Resta, May 08 2017 LINKS Amiram Eldar, Table of n, a(n) for n = 1..36 (calculated using data from Jud McCranie) FORMULA For n > 3, a(n) = A055234(n). - David Wasserman, Aug 18 2005 MATHEMATICA ds[x_, de_] := DivisorSigma[1, x]-de*EulerPhi[x] a[n_] := Block[{m=1, s=ds[m, n]}, While[(s !=0||PrimeQ[m])&&!Greater[m, 100000], m++ ]; m]; Table[a[n], {n, 22}] CROSSREFS Compare A087979, which has a slightly different definition. Cf. A074891, A000203, A000010, A087979, A020492. Cf. A055234. Sequence in context: A051050 A267198 A267140 * A033355 A267402 A217408 Adjacent sequences:  A088827 A088828 A088829 * A088831 A088832 A088833 KEYWORD nonn AUTHOR Labos Elemer, Nov 03 2003 EXTENSIONS More terms from David Wasserman, Aug 18 2005 a(32) from Donovan Johnson, Sep 03 2013 a(33) from Giovanni Resta, May 08 2017 STATUS approved

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Last modified April 15 23:45 EDT 2021. Contains 343015 sequences. (Running on oeis4.)