A274173 Numbers n such that n is not divisible by 5 and n^k is of the form a^2 + b^4 for all k not divisible by 4.

609076, 9745216, 28998521, 36924641

Offset

1,1

Comments

Numbers n such that n, n^2 and n^3 is in A111925 and n is not divisible by 5.

Since there cannot be fourth power in A111925, this sequence focuses on the values of k that is not divisible by 4 in definition.

Links

Table of n, a(n) for n=1..4.

Example

609076 is a term because 609076 = 710^2 + 18^4, 609076^2 = 581940^2 + 424^4, 609076^3 = 475342920^2 + 676^4 and it is not divisible by 5.

Prog

(PARI) isA111925(n) = for(b=1, sqrtnint(n-1, 4), if(issquare(n-b^4), return(1))); 0;
isok(n) = n%5 != 0 && isA111925(n) && isA111925(n^2) && isA111925(n^3);

Crossrefs

Cf. A111925.

Sequence in context: A351721 A340924 A218107 * A206175 A205429 A308279

Adjacent sequences: A274170 A274171 A274172 * A274174 A274175 A274176

Keyword

nonn,more

Author

Altug Alkan, Jun 12 2016

Status

approved