OFFSET
1,2
LINKS
Petros Hadjicostas, Table of n, a(n) for n = 1..500
FORMULA
EXAMPLE
n = 3: a(1) = 1, a(2) = 3, s = 1 + 3 = 4; n1 = 5 and n2 = 7 (not 6) are both coprime to s, hence a(3) = n1 + n2 = 12;
n = 4: a(1) = 1, a(2) = 3, a(3) = 12, s = 1 + 3 + 12 = 16; n1 = 13 and n2 = 15 (not 14) are both coprime to s, hence a(4) = n1 + n2 = 28;
n = 5: s = 44; n1 = 29 and n2 = 31 are both coprime to s, hence a(5) = n1 + n2 = 60;
n = 6: s = 104; n1 = 61 and n2 = 63 are both comprime to s, hence a(6) = n1 + n2 = 124.
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, 3], val); print1(v[1], ", ", v[2], ", "); for (n=3, nn, val = findnext(v[#v], vecsum(v)); v = concat(v, val); print1(val, ", "); ); } \\ [Modification of Michel Marcus's PARI program from sequence A131357]
CROSSREFS
KEYWORD
nonn
AUTHOR
Petros Hadjicostas, Jun 25 2019
STATUS
approved