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

 

Logo

Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A175070 a(n) is the sum of perfect divisors of n - n, where a perfect divisor of n is a divisor d such that d^k = n for some k >= 1. 3
0, 0, 0, 2, 0, 0, 0, 2, 3, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 3, 0, 0, 0, 0, 2, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(1) = 0, for n >=2: a(n) = sum of perfect divisors of n less than n.

a(n) > 0 for perfect powers n = A001597(m) for m > 2.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for sequences related to sums of divisors

FORMULA

a(n) = A175067(n) - n.

PROG

(PARI) A175070(n) = if(!ispower(n), 0, sumdiv(n, d, if((d>1)&&(d<n)&&((d^valuation(n, d))==n), d, 0))); \\ Antti Karttunen, Jun 12 2018

(PARI) first(n) = {my(res = vector(n)); for(i = 2, sqrtint(n), for(j = 2, logint(n, i), res[i^j] += i)); res} \\ David A. Corneth, Jun 12 2018

CROSSREFS

Cf. A175067.

Sequence in context: A210703 A275964 A284272 * A054923 A263145 A057108

Adjacent sequences:  A175067 A175068 A175069 * A175071 A175072 A175073

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Jan 23 2010

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 15 11:05 EST 2018. Contains 318148 sequences. (Running on oeis4.)