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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A227758 a(n) = sigma(sigma(n)) - sigma(n) - n, where sigma(n) = A000203(n) = sum of the divisors of n. 4
-1, -1, 0, -3, 1, 10, 0, 1, -8, 11, 5, 16, -3, 22, 21, -15, 4, -1, 3, 34, 10, 33, 13, 84, -24, 28, 23, 36, 13, 93, 0, 9, 43, 32, 41, -15, -15, 70, 25, 104, 13, 114, -3, 96, 45, 77, 29, 52, -26, -15, 72, 21, 13, 186, 68, 184, 49, 86, 49, 252, -27, 94, 43, -63 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Conjecture: a(n) = 0 for Mersenne primes (A000668). [This is easily proved: For Mersenne primes n=2^p-1, sigma(n)=n+1=2^p, sigma(2^p)=2^(p+1)-1, thus a(n)=0. - M. F. Hasler, Jul 30 2013]

a(n) <  0 for numbers n from A227759, a(n) >  0 for numbers n from A227760.

Sequence contains anomalous increased frequency of values 13 (see A227756).

LINKS

Paul Tek, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A051027(n) - A000203(n) - n.

EXAMPLE

For n = 6; a(n) = sigma(sigma(6)) - sigma(6) - 6 = 28 - 12 - 6 = 10.

CROSSREFS

Cf. A051027, A000203, A000668, A227759, A227760, A227756.

Sequence in context: A128415 A227795 A090479 * A304638 A141903 A010289

Adjacent sequences:  A227755 A227756 A227757 * A227759 A227760 A227761

KEYWORD

sign

AUTHOR

Jaroslav Krizek, Jul 26 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 November 26 09:38 EST 2020. Contains 338639 sequences. (Running on oeis4.)