OFFSET
1,1
LINKS
Joerg Arndt, Matters Computational (The Fxtbook).
Eric Weisstein's World of Mathematics, Hadamard Matrix.
Eric Weisstein's World of Mathematics, Paley Class.
FORMULA
Divisible by 4 but not of form 2^a*(q+1), q = odd prime power.
PROG
(PARI) isp(k) = for (i=0, valuation(k, 2), if (isprimepower(k/2^i-1, &p) && (p%2), return(1)); ); return(0);
isok(k) = !(k%4) && !isp(k); \\ Michel Marcus, Mar 05 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved