OFFSET
1,3
COMMENTS
This sequence appears to be dense in semiprimes.
LINKS
R. J. Cano, Table of n, a(n) for n = 1..100
MATHEMATICA
Table[Mod[Sum[2^(Prime[k] - 1), {k, n}], n!]/2, {n, 23}] (* Michael De Vlieger, Sep 09 2015 *)
PROG
(PARI) a(n)=sum(k=1, n, 2^(prime(k)-1))%n!/2
for(i=1, 30, print1(a(i), ", ")); \\ R. J. Cano, Sep 08 2015
(Magma) [(&+[2^(NthPrime(k)-1): k in [1..n]] mod Factorial(n))/2: n in [1..25]]; // Bruno Berselli, Sep 24 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
R. J. Cano and M. F. Hasler, Sep 08 2015
STATUS
approved