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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 20 14:26 EST 2020. Contains 331094 sequences. (Running on oeis4.)