The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A137818 Non-biquadratefree "year numbers": phi(n) = 2 phi(sigma(n)) and p^4 | n for some p>1. 2
 295569, 1811079, 1964375, 2069469, 4473387, 5854375, 10936053, 13260625, 18029709, 21576537, 22182093, 25536875, 35595625, 46404333, 49648383, 55094375, 57044817, 58650625, 67009923, 69166467, 72681875, 76106875 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS See A137815 for general comments and references about "year numbers". This is the subsequence of elements of A137815 divisible by a biquadrateful number, i.e. its intersection with A046101 (numbers divisible by the 4th power of some prime). As such, it is of course also a subsequence of A137817 and a fortiori of A137816. There are only 28 such numbers below 10^8. LINKS Donovan Johnson, Table of n, a(n) for n = 1..500 PROG (PARI) for( i=1, #A137816, vecmax( factor( A137816[i])[, 2])>3 && print1(A137816[i]", ")) (PARI) for( i=1, #A046099, eulerphi(A046099[i])==2*eulerphi(sigma(A046099[i])) && print1( A046099[i] ", ")) (PARI) for( n=1, 10^9, issquarefree(n) && next; vecmax(factor(n)[, 2])>3 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", ")) CROSSREFS Cf. A137815-A137819, A046101. Sequence in context: A254919 A109031 A137817 * A303357 A251387 A164946 Adjacent sequences: A137815 A137816 A137817 * A137819 A137820 A137821 KEYWORD nonn AUTHOR R. K. Guy, R. J. Mathar and M. F. Hasler, Feb 11 2008 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 7 15:01 EST 2022. Contains 358667 sequences. (Running on oeis4.)