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!)
A070007 Arithmetic mean of distinct primes dividing n is a square number. 4
15, 42, 45, 65, 75, 77, 84, 87, 126, 135, 141, 168, 225, 247, 252, 258, 261, 285, 294, 301, 325, 335, 336, 357, 375, 378, 405, 410, 423, 429, 481, 504, 516, 539, 588, 589, 591, 618, 671, 672, 675, 717, 756, 767, 774, 783, 785, 820, 845, 847, 855, 882, 986 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subset of A078174. [R. J. Mathar, Sep 20 2008]

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

EXAMPLE

n=1972=2*17*29: mean=(2+17+29)/3=48/3=16, a square.

MATHEMATICA

Select[Range[2, 1000], IntegerQ@ Sqrt[Total[First /@ FactorInteger@ #]/PrimeNu@ #] &] (* Michael De Vlieger, Mar 28 2015 *)

PROG

(PARI) lista(nn) = {for (n=2, nn, f = factor(n); if ((#f~ != 1) && (type(q=sum(k=1, #f~, f[k, 1])/#f~) == "t_INT") && issquare(q), print1(n, ", ")); ); } \\ Michel Marcus, Mar 28 2015

CROSSREFS

Cf. A070005, A070006, A001414, A008472.

Sequence in context: A239325 A024845 A056698 * A325041 A154267 A173351

Adjacent sequences:  A070004 A070005 A070006 * A070008 A070009 A070010

KEYWORD

nonn

AUTHOR

Labos Elemer, Apr 11 2002

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 September 27 08:39 EDT 2021. Contains 347689 sequences. (Running on oeis4.)