A237046 Numbers n such that sigma(n) < 2n-1.

3, 5, 7, 9, 10, 11, 13, 14, 15, 17, 19, 21, 22, 23, 25, 26, 27, 29, 31, 33, 34, 35, 37, 38, 39, 41, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 55, 57, 58, 59, 61, 62, 63, 65, 67, 68, 69, 71, 73, 74, 75, 76, 77, 79, 81, 82, 83, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97, 98, 99, 101

Offset

1,1

Comments

Numbers n such that A235796(n) > 0.

Complement of A103288.

If the only least-deficient numbers are the powers of 2 (which is an open problem) then the union of A000079 and A023196 and this sequence gives A000027 (see also A103288).

Links

Table of n, a(n) for n=1..70.

Example

10 is in the sequence because the sum of divisors of 10 is less than (2*10 - 1). The sum of divisors of 10 is 1 + 2 + 5 + 10 = 18 and 2*10 - 1 = 19.

Mathematica

Select[Range[120], DivisorSigma[1, #]<2#-1&] (* Harvey P. Dale, Sep 12 2018 *)

Prog

(PARI) s=[]; for(n=1, 200, if(sigma(n)<2*n-1, s=concat(s, n))); s \\ Colin Barker, Feb 20 2014

Crossrefs

Cf. A000203, A005100, A023196, A033879, A103288, A196020, A235796, A236104.

Sequence in context: A365830 A238524 A237287 * A370421 A076212 A085621

Adjacent sequences: A237043 A237044 A237045 * A237047 A237048 A237049

Keyword

nonn,easy

Author

Omar E. Pol, Feb 19 2014

Status

approved