OFFSET
0,2
LINKS
Erdős Pál, "Ramanujan and I" Number Theory, Madras 1987. Springer, Berlin, Heidelberg, 1989. 1-17.
Leo Moser, "On the product of the primes not exceeding n", Canad. Math. Bull. 2 (1959), 119 - 121.
FORMULA
a(n) = 4^n - n#, where n# is the product of primes less than or equal to n (see A034386).
EXAMPLE
4^5 = 1024. The primes less than or equal to 5 are 2, 3, and 5. Then 2 * 3 * 5 = 30 and hence a(5) = 1024 - 30 = 994.
MAPLE
restart;
with(NumberTheory);
a := n -> 4^n-product(ithprime(i), i = 1 .. PrimeCounting(n)):
0, seq(a(n), n = 1 .. 15); # Stefano Spezia, Nov 06 2018
MATHEMATICA
Table[4^n - Times@@Select[Range[n], PrimeQ], {n, 0, 31}]
PROG
(PARI) a034386(n) = my(v=primes(primepi(n))); prod(i=1, #v, v[i]) \\ after Charles R Greathouse IV in A034386
a(n) = 4^n - a034386(n) \\ Felix Fröhlich, Nov 04 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Alonso del Arte, Sep 29 2018
STATUS
approved