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A162930 Primes that can be written as a sum of a positive square and a positive cube in more than one way. 2

%I #24 Jul 02 2023 09:09:06

%S 17,89,233,449,577,593,1289,1367,1601,1753,2089,2521,3391,4481,4721,

%T 5953,6121,6427,7057,7577,8081,9649,10313,10657,10729,11969,12329,

%U 13121,13457,15137,15193,15641,15661,16033,16649,18523,21673,21961,23201

%N Primes that can be written as a sum of a positive square and a positive cube in more than one way.

%C A subset of these, 2089, 4481, 7057, 15193, 15641, etc., allows this representation in more than two ways (See A206606).

%H David A. Corneth, <a href="/A162930/b162930.txt">Table of n, a(n) for n = 1..10808</a> (first 500 terms from Seiichi Manyama, terms <= 8*10^7)

%F A000040 INTERSECT A054402.

%e The prime 17 can be written 1^3 + 4^2 as well as 2^3 + 3^2.

%p isA162930 := proc(n) if isprime(n) then wa := 0 ; for y from 1 to n/2 do if issqr(n-y^3) then if n -y^3 > 0 then wa := wa+1 ; fi; fi; od: RETURN( wa>1) ; else false; fi; end:

%p for i from 1 to 2700 do if isA162930 ( ithprime(i)) then printf("%d,",ithprime(i)) ; fi; od: # _R. J. Mathar_, Jul 21 2009

%t lst={};Do[Do[AppendTo[lst,n^2+m^3],{n,2*5!}],{m,2*5!}];lst=Sort[lst]; lst2={};Do[If[lst[[n]]==lst[[n+1]]&&PrimeQ[lst[[n]]],AppendTo[lst2, lst[[n]]]],{n,Length[lst]-1}];lst2;

%o (PARI) upto(n) = {my(res = List(), v = vector(n), i, j, i2); for(i = 1, sqrtint(n), i2 = i^2; for(j = 1, sqrtnint(n - i^2, 3), v[i2 + j^3]++)); forprime(p = 2, n, if(v[p] > 1, listput(res, p))); kill(v); res} \\ _David A. Corneth_, Jun 20 2023

%Y Cf. A000040, A054402, A123364, A123388, A173795, A206606.

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Jul 17 2009

%E Slightly edited by _R. J. Mathar_, Jul 21 2009

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)