login
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
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. A055234.
Sequence in context: A267198 A267140 A348893 * A033355 A267402 A217408
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