A331521 - OEIS

%I #15 Jan 20 2020 12:53:23

%S 1,1,2,1,3,2,4,1,2,4,6,3,5,2,8,7,2,4,6,9,4,10,5,12,8,1,3,5,13,11,2,4,

%T 14,5,7,11,14,2,6,8,10,16,12,1,3,9,14,10,17,16,2,4,8,15,10,17,1,7,11,

%U 13,18,6,8,12,3,7,19,9,11,2,19,16,1,9,13,12,23

%N a(n) is the least positive k such that A002645(n) - k^4 is a fourth power.

%H Rémy Sigrist, <a href="/A331521/b331521.txt">Table of n, a(n) for n = 1..10000</a>

%H Rémy Sigrist, <a href="/A331521/a331521_1.gp.txt">PARI program for A331521</a>

%e The first terms, alongside A002645(n), are:

%e   n   a(n)  A002645(n)

%e   --  ----  ----------------

%e    1     1     2 = 1^4 + 1^4

%e    2     1    17 = 1^4 + 2^4

%e    3     2    97 = 2^4 + 3^4

%e    4     1   257 = 1^4 + 4^4

%e    5     3   337 = 3^4 + 4^4

%e    6     2   641 = 2^4 + 5^4

%e    7     4   881 = 4^4 + 5^4

%e    8     1  1297 = 1^4 + 6^4

%e    9     2  2417 = 2^4 + 7^4

%e   10     4  2657 = 4^4 + 7^4

%o (PARI) See Links section.

%Y See A331435 for similar sequences.

%Y Cf. A000583, A002645.

%K nonn

%O 1,3

%A _Rémy Sigrist_, Jan 19 2020