login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A259124 If n is representable as x*y+x+y, with x>=y>1, then a(n) is the sum of all x's and y's in all such representations. Otherwise a(n)=0. 4
0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 5, 0, 0, 6, 6, 0, 7, 0, 7, 8, 0, 0, 17, 8, 0, 10, 9, 0, 20, 0, 10, 12, 0, 10, 34, 0, 0, 14, 23, 0, 26, 0, 13, 28, 0, 0, 43, 12, 13, 18, 15, 0, 32, 14, 29, 20, 0, 0, 67, 0, 0, 36, 32, 16, 38, 0, 19, 24, 32, 0, 76, 0, 0, 44, 21, 16, 44, 0, 57, 44 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,8

COMMENTS

The sequence of numbers that never appear in a(n) begins: 1, 2, 3, 11, 27, 35, 51, 53, 79, 83, 89, 93, 117, 123, 125, 135, 143, 145.

The indices n at which a(n)=0 are in A254636. - Vincenzo Librandi, Jul 16 2015

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = Sum({d: d | n+1 and 3 <= d <= sqrt(n+1)}, d + (n+1)/d - 2). - Robert Israel, Aug 05 2015

EXAMPLE

11 = 3*2 + 3 + 2, so a(11)=5.

MAPLE

f:= proc(n) local D, d;

      D:= select(t -> (t >= 3 and t^2 <= n+1), numtheory:-divisors(n+1));

      add(d + (n+1)/d - 2, d = D);

end proc:

map(f, [$1..100]); # Robert Israel, Aug 05 2015

PROG

(Python)

TOP = 100

a = [0]*TOP

for y in range(2, TOP/2):

for x in range(y, TOP/2):

    n = x*y + x + y

    if n>=TOP: break

    a[n] += x+y

print a

(PARI) a(n)=sum(y=2, sqrtint(n+1)-1, my(x=(n-y)/(y+1)); if(denominator(x)==1, x+y)) \\ Charles R Greathouse IV, Jun 29 2015

CROSSREFS

Cf. A254636, A255361.

Sequence in context: A189885 A151673 A005397 * A273515 A308225 A021718

Adjacent sequences:  A259121 A259122 A259123 * A259125 A259126 A259127

KEYWORD

nonn,changed

AUTHOR

Alex Ratushnyak, Jun 18 2015

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 December 12 12:50 EST 2019. Contains 329958 sequences. (Running on oeis4.)