OFFSET
1,1
COMMENTS
For all n>=1, a(n)>=2.
EXAMPLE
For n=3, prime(3)=5. The only integers k <= 5^2 such that A075860(k)=5 are 5,6,12,18,24 and 25. Therefore a(3)=6.
MAPLE
f := proc (n)
option remember;
if isprime(n) then
return n
else
return procname(convert(numtheory:-factorset(n), `+`))
end if
end proc:
g := proc (n)
local count, k;
count := 0;
for k from ithprime(n) to ithprime(n)^2 do
if f(k) = ithprime(n) then
count := count + 1
end if
end do;
return count
end proc:
map(g, [$1 .. 80]);
PROG
(PARI) fp(n, pn) = if (n == pn, n, fp(vecsum(factor(n)[, 1]), n));
f(n) = if (n==1, 0, fp(n, 0)); \\ A075860
a(n) = sum(k=1, prime(n)^2, f(k) == prime(n)); \\ Michel Marcus, Jul 04 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Rafik Khalfi, Jul 04 2024
STATUS
approved