A381725 - OEIS

A381725

Numbers k such that 5^k - 4^k is a semiprime.

2, 5, 7, 11, 13, 19, 31, 41, 79, 83, 113, 157, 173, 233, 281, 317, 359, 373

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OFFSET

1,1

COMMENTS

Are all terms prime? Any term that is not a prime must be the square of a member of A059802.

LINKS

FORMULA

EXAMPLE

a(3) = 7 is a term because 5^7 - 4^7 = 61741 = 29 * 2129 with 29 and 2129 prime.

MAPLE

filter:= n -> numtheory:-bigomega(5^n - 4^n):

select(filter, [2, seq(i, i=3..120, 2]);

CROSSREFS

KEYWORD

nonn,hard,more,new

AUTHOR

EXTENSIONS

a(14)-a(18) from Jinyuan Wang, Mar 05 2025

STATUS

approved