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A262016 a(n) = ( ( Sum_{k=1..n} 2^(prime(k)-1) ) mod n! ) / 2. 1
0, 0, 2, 7, 15, 83, 91, 5163, 86315, 401323, 14725035, 65973803, 2562459691, 37695987243, 45627576875, 9183900142123, 39579412285995, 2598666482813483, 28017829467228715, 223446104928848427, 275288604322335275, 116723151945719253547, 12606804937123633465899 (list; graph; refs; listen; history; text; internal format)
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

Sequence in context: A050612 A120110 A047694 * A129666 A288675 A135781

Adjacent sequences:  A262013 A262014 A262015 * A262017 A262018 A262019

KEYWORD

nonn

AUTHOR

R. J. Cano and M. F. Hasler, Sep 08 2015

STATUS

approved

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Last modified January 23 01:30 EST 2020. Contains 331166 sequences. (Running on oeis4.)