

A228450


Deficient numbers with increasing abundancy without being powers of 2.


3



3, 9, 10, 44, 110, 136, 592, 884, 2144, 8384, 18632, 32896, 116624, 391612, 527872, 1090912, 2102272, 8394752, 15370304, 73995392, 536920064, 815634435, 2147516416, 34360131584, 217898810368, 546409576448, 549759483904
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OFFSET

1,1


COMMENTS

Without the additional condition one would have obtained A000079, see "last deficient comment there. Subsequence of A005100.


LINKS

Table of n, a(n) for n=1..27.


EXAMPLE

First term is 3 with sigma(n)/n = 4/3 ~ 1.33, then 4 with 13/9 ~ 1.44, then 10 with 9/5 = 1.80.


MATHEMATICA

abun[n_] := DivisorSigma[1, n]/n; mx = 0; t = {}; Do[m = abun[n]; If[m < 2 && m > mx && ! IntegerQ[Log[2, n]], mx = m; AppendTo[t, n]], {n, 10000}]; t (* T. D. Noe, Apr 09 2014 *)


PROG

(PARI) lista(nn) = {rab = 0; for (n=1, nn, if (n != 2^valuation(n, 2), ab = sigma(n)/n; if ((ab < 2) && (ab > rab), print1(n, ", "); rab = ab; ); ); ); } \\ Michel Marcus, Oct 27 2013


CROSSREFS

Cf. A000079, A000203, A005100, A071927, A171929, A188597.
Sequence in context: A031115 A004669 A173242 * A121057 A025538 A070354
Adjacent sequences: A228447 A228448 A228449 * A228451 A228452 A228453


KEYWORD

nonn,more


AUTHOR

Michel Marcus, Oct 27 2013


EXTENSIONS

a(21)a(22) from Michel Marcus, Oct 28 2013
a(23)a(27) from Donovan Johnson, Nov 13 2013


STATUS

approved



