login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A227759 Numbers n such that A227758(n) = sigma(sigma(n)) - sigma(n) - n < 0, where sigma(n) = A000203(n) = sum of the divisors of n 2
1, 2, 4, 9, 13, 16, 18, 25, 36, 37, 43, 49, 50, 61, 64, 67, 73, 81, 97, 98, 100, 109, 121, 144, 151, 157, 163, 169, 181, 193, 211, 225, 229, 241, 242, 256, 277, 283, 289, 313, 324, 331, 337, 338, 361, 373, 397, 400, 409, 421, 433, 441, 457, 484, 487, 523, 529 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that A051027(n) - A000203(n) - n < 0, where A000203(n) = sum of the divisors of n , A051027(n) = A000203(A000203(n)) = sigma(sigma(n)) = sum of the divisors of the sum of the divisors of n.

Conjecture: a(n) = complement of union A000668 and A227760, where A000668 = Mersenne primes, A227760 = numbers n such that sigma(sigma(n)) - sigma(n) - n > 0.

LINKS

Table of n, a(n) for n=1..57.

FORMULA

A227758(a(n)) < 0.

EXAMPLE

Number 16 is in sequence because sigma(sigma(16)) - sigma(16) - 16 = 32 - 31 - 16 = -15 < 0.

CROSSREFS

Cf. A000203, A051027, A000668, A227760, A227758.

Sequence in context: A098009 A129376 A266582 * A320514 A210640 A024925

Adjacent sequences:  A227756 A227757 A227758 * A227760 A227761 A227762

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Jul 29 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 21 02:20 EST 2021. Contains 340332 sequences. (Running on oeis4.)