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!)
A325470 a(n) is the sum of divisors d of n such that d divides sigma(d). 4
1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 29, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 29, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 35, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..20000

FORMULA

a(A097603(n)) > 1.

EXAMPLE

For n = 12, divisors d of 12: 1, 2, 3, 4, 6, 12; corresponding sigma(d): 1, 3, 4, 7, 12, 28; d divides sigma(d) for 2 divisors d: 1 and 6; a(12) = 1 + 6 = 7.

MATHEMATICA

a[n_] := DivisorSum[n, # &, Divisible[DivisorSigma[1, #], #] &];  Array[a, 100] (* Amiram Eldar, Aug 17 2019 *)

PROG

(MAGMA) [&+[d: d in Divisors(n) | IsIntegral(SumOfDivisors(d) / d)] : n in [1..100]]

(PARI) a(n)={sumdiv(n, d, if(sigma(d) % d == 0, d))} \\ Andrew Howroyd, Aug 16 2019

CROSSREFS

Cf. A000203, A097603, A325469, A325471.

Sequence in context: A101027 A129408 A339748 * A240831 A170824 A248909

Adjacent sequences:  A325467 A325468 A325469 * A325471 A325472 A325473

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Aug 16 2019

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 June 14 19:28 EDT 2021. Contains 345038 sequences. (Running on oeis4.)