OFFSET
1,2
LINKS
Michel Marcus, Table of n, a(n) for n = 1..1000
FORMULA
Conjecture: a(n) ~ 2^(n+1) * 0.9873393997556885598467... - Petros Hadjicostas, Jun 23 2019 [Constant evaluated using Michel Marcus's bfile]
EXAMPLE
n = 3: a(1) = 1, a(2) = 2, s = 1 + 2 = 3; n1 = 4 (not 3) and n2 = 5 are both coprime to s, hence a(3) = n1 + n2 = 9;
n = 4: a(1) = 1, a(2) = 2, a(3) = 9, s = 1 + 2 + 9 = 12; n1 = 11 (not 10 or 12) and n2 = 13 are both coprime to s, hence a(4) = n1 + n2 = 24;
n = 5: s = 36; n1 = 25 (not 26, 27, or 28) and n2 = 29 are both coprime to s, hence a(5) = n1 + n2 = 54;
n = 6: s = 90; n1 = 59 (not 55, 56, 57, 58, or 60) and n2 = 61 are both comprime to s, hence a(6) = n1 + n2 = 120.
PROG
(PARI) findnext(last, s) = {my(x = last+1); while (gcd(x, s) != 1, x++); my(y = x+1); while (gcd(y, s) != 1, y++); x+y; }
lista(nn) = {my(v = [1, 2], val); print1(v[1], ", ", v[2], ", "); for (n=3, nn, val = findnext(v[#v], vecsum(v)); v = concat(v, val); print1(val, ", "); ); } \\ Michel Marcus, Jun 25 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Sep 30 2007
EXTENSIONS
More terms from Petros Hadjicostas, Jun 23 2019
STATUS
approved