A137365: correct terms?

Maximilian Hasler maximilian.hasler at gmail.com
Sun Apr 13 04:03:29 CEST 2008


zs> %N A137365 Prime numbers n such that n = p1^3 + p2^3 +
zs> p3^3, a sum of cubes of 3 distinct prime  numbers.
rm>  Having run the code below up to 87697, I confirm Zak's improved sequence
rm>  of A137365

As usual I also confirm the results, a bit late and using PARI code given below.
I'll submit it as correctly formatted COMMENT to Neil, including a b-file
of the 327 terms <= 10^6 (takes less than 30 sec. on my laptop).

For naming my isAxxx function, I'd like to find either of the sequences:

Axxx = numbers which are the sum of the cubes of 3 different odd primes
 =?= 495,1483,1701,1799,2349,2567,2665,3555,3653,3871,5065...
or
Ayyy = numbers which are the sum of the cubes of 3 different primes
 =?= 160,378,476,495,1366,1464,1483,1682,1701,1799,2232,2330,2349,2548...

 (The former might seem a bit artificial, but in fact the latter is
the former plus
additional terms which are even numbers N such that N-8 is in the sequence

Azzz = sums of 2 cubes of distinct odd primes
 =?= 3^3+5^3, 3^3+7^3, 5^3+7^3, 3^3+11^3, 5^3+11^3,...
 = 152, 370, 468, 1358, 1456...

To my great surprise, none of these seem to exist... (not even 152,370 is found)
(I can't believe it so I put =?= to mean that my terms may be wrong.)

If somebody spots an error in my values, please let me know.
(Else I consider submitting them unless I'm told I shouldn't.)

\\ Axxx = numbers which are the sum of 3 cubes of distinct odd primes
isAxxx(n)={ local( c,d); forprime( p=floor( sqrtn( n\3+1,3))+1, floor(
sqrtn( n-151,3)),
 d=n-p^3; forprime( q=floor( sqrtn( d\2+1,3))+1, min( p-1, floor(
sqrtn( d-26,3))),
  round( sqrtn( c=d-q^3,3 ))^3==c | next; isprime( round( sqrtn( c,3
))) & return(1)))}

forprime(p=3^3+5^3+7^3,10^5,isAxxx(p)|next; print1(p",")) \\ this is A137365

1483,5381,6271,7229,9181,11897,13103,13841,14489,17107,20357,25747,26711,27917,30161,30259,31247,32579,36161,36583,36677,36899,36901
,42083,48817,54181,55511,55691,56377,56897,57637,59093,64151,66347,67733,69073,69389,74177,75167,76031,76123,77239,77977,80471,80963
,81181,81901,85751,86491,87697,93337,93871,95507,96587,98533,98837,
time = 1,750 ms.





More information about the SeqFan mailing list