A331521 a(n) is the least positive k such that A002645(n) - k^4 is a fourth power.

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

Offset

1,3

Links

Rémy Sigrist, Table of n, a(n) for n = 1..10000

Rémy Sigrist, PARI program for A331521

Example

The first terms, alongside A002645(n), are:
  n   a(n)  A002645(n)
  --  ----  ----------------
   1     1     2 = 1^4 + 1^4
   2     1    17 = 1^4 + 2^4
   3     2    97 = 2^4 + 3^4
   4     1   257 = 1^4 + 4^4
   5     3   337 = 3^4 + 4^4
   6     2   641 = 2^4 + 5^4
   7     4   881 = 4^4 + 5^4
   8     1  1297 = 1^4 + 6^4
   9     2  2417 = 2^4 + 7^4
  10     4  2657 = 4^4 + 7^4

Prog

(PARI) See Links section.

Crossrefs

See A331435 for similar sequences.

Cf. A000583, A002645.

Sequence in context: A336395 A336393 A332899 * A244967 A124172 A349191

Adjacent sequences: A331518 A331519 A331520 * A331522 A331523 A331524

Keyword

nonn

Author

Rémy Sigrist, Jan 19 2020

Status

approved