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A339327
a(n) = (A001414(prime(n)-1)*A001414(prime(n)+1)) mod prime(n).
2
0, 2, 0, 2, 5, 11, 13, 15, 2, 23, 7, 25, 9, 8, 40, 28, 18, 30, 1, 26, 30, 76, 21, 43, 14, 5, 6, 73, 16, 21, 83, 98, 96, 31, 19, 73, 50, 141, 24, 41, 112, 149, 8, 134, 145, 105, 125, 45, 39, 93, 36, 177, 143, 38, 254, 30, 60, 129, 75, 93, 221, 291, 243, 214, 55, 59, 172, 167, 54, 335, 285, 205
OFFSET
1,2
COMMENTS
a(n)=1 for n=19 and 7476. Are there others?
LINKS
EXAMPLE
a(4) = (A001414(6)*A001414(8)) mod 7 = (5*6) mod 7 = 2.
MAPLE
spf:= proc(n) add(t[1]*t[2], t=ifactors(n)[2]) end proc:
f:= proc(n) local p;
p:= ithprime(n);
spf(p-1)*spf(p+1) mod p
end proc:
map(f, [$1..100]);
CROSSREFS
Cf. A001414.
Sequence in context: A175631 A243816 A243159 * A258144 A113772 A033716
KEYWORD
nonn,look
AUTHOR
J. M. Bergot and Robert Israel, Nov 30 2020
STATUS
approved