A329983 For any n > 0, define the sequence b(1) = n, b(i+1) = (b(i) * i) mod (b(i) + i); a(n) is the least i such that b(i) = 0, or -1 if 0 is never reached.

1, 13, 3, 85, 13, 85, 7, 58, 4, 13, 7, 85, 5, 7, 13, 58, 58, 85, 85, 13, 5, 85, 7, 291, 13, 85, 58, 85, 58, 7, 85, 291, 85, 85, 13, 58, 13, 58, 291, 11, 6, 58, 13, 7, 13, 85, 7, 291, 58, 85, 9, 85, 7, 13, 13, 58, 85, 13, 9, 58, 291, 291, 13, 11

Offset

0,2

Links

Rémy Sigrist, Table of n, a(n) for n = 0..10000

Prog

(Python) def k(a, b):
    return ((a*b)%(a+b))
numberList=[]
def repeat(a):
    i=1
    while a!=0:
        a= k(a, i)
        i=i+1
    numberList.append(i)
for x in range(10000):
    repeat(x)
print(numberList)
(PARI) f(m, n) = (m*n) % (m+n);
a(n) = {my(i=1); while (n, n = f(n, i); i++; ); i; } \\ Michel Marcus, Nov 28 2019

Crossrefs

Cf. A308651.

Sequence in context: A297874 A298137 A155847 * A204594 A204157 A010219

Adjacent sequences: A329980 A329981 A329982 * A329984 A329985 A329986

Keyword

nonn

Author

Stefan Gog, Nov 26 2019

Status

approved