|
Search: id:A114931
|
|
|
| A114931 |
|
Numbers n such that phi(n)=4*reversal(n). |
|
+0
2
|
|
| 10, 20, 40, 50, 80, 210, 420, 630, 711, 831, 840, 2910, 29910, 40320, 80640, 98361, 673140, 865580, 8656341, 466760130
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
If p=10^m-3 is prime then 30*p is in the sequence because phi(30*p)=phi(30)*phi(p)=8*(10^m-4)=4*(2*10^m-8)=4*reversal (3*10^m-9)=4*reversal(3*p)=4*reversal(30*p). Next term is greater than 55*10^7.
|
|
EXAMPLE
|
466760130 is in the sequence because phi(466760130)=4*31067664
=4*reversal(466760130).
|
|
MATHEMATICA
|
Do[If[EulerPhi[n]==4*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 550000000}]
|
|
CROSSREFS
|
Cf. A069215, A114930.
Sequence in context: A047881 A020953 A033846 this_sequence A013978 A053162 A110804
Adjacent sequences: A114928 A114929 A114930 this_sequence A114932 A114933 A114934
|
|
KEYWORD
|
base,more,nonn
|
|
AUTHOR
|
Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 29 2006
|
|
|
Search completed in 0.002 seconds
|
