|
Search: id:A134038
|
|
|
| A134038 |
|
Mersenne indices of Mersenne prime reversals which are odd composites (associated with A134039). |
|
+0
3
|
| |
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
Suggested by Puzzle 417 of Carlos Rivera's The Prime Puzzles & Problems Connection The program below, slightly modified, was used to find the first prime divisor of the Mersenne reversal if an odd composite
|
|
FORMULA
|
Generate the Mersenne primes, reverse; if the reversal is an odd composite find the first prime divisor associated with the Mersenne index number
|
|
EXAMPLE
|
The Mersenne index 4 is that of 2^7-1 = 127. The reversal is 721 whose first prime divisor is 7, and 7*103=721.
|
|
PROGRAM
|
UBASIC for a(4): 10 'primes using counters 20 N=727501488517303786137132964064381141071 30 A=3:S=sqrt(N):C="c" 40 B=N\A 50 if B*A=N then print B; A; N; "-"; :N=N+2:goto 30 60 A=A+2 70 if A<=sqrt(N) then 40 80 if N>2 then stop 81 C=C+1 90 print C; N; "-"; 100 N=N+2:goto 30
|
|
CROSSREFS
|
Cf. A134039 A134037.
Sequence in context: A129235 A012903 A013018 this_sequence A031271 A126591 A031452
Adjacent sequences: A134035 A134036 A134037 this_sequence A134039 A134040 A134041
|
|
KEYWORD
|
more,nonn
|
|
AUTHOR
|
Enoch Haga (Enokh(AT)comcast.net), Oct 02 2007
|
|
|
Search completed in 0.002 seconds
|
