OFFSET
1,4
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(8) = 3 because prime(8) = 19 and there are 3 pairs (3,2), (7,2), (11,3) with 3 | 2+19, 2 | 3+19, 7 | 2+19, 2 | 7+19, 11 | 3+19, 3 | 11+19.
MAPLE
f:= proc(n) local ia, a, b, c, t;
c:= ithprime(n);
t:= 0;
for ia from 1 to n-1 do
a:= ithprime(ia);
t:= t + nops(select(b -> b < c and b+c mod a = 0, numtheory:-factorset(a+c)))
od;
t/2
end proc:
map(f, [$1..100]);
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, May 28 2021
STATUS
approved