A151413 Index at which n occurs in A160256, or -1 if n never occurs.

1, 2, 3, 4, 14, 5, 20, 6, 7, 12, 32, 11, 301, 22, 16, 8, 1065, 9

Offset: 1

Author

N. J. A. Sloane, May 16 2009

Keywords

• nonn
• more

Comments

After a(19) which exceeds 10^7 but is still unknown, the sequence continues 18,24,34,a(23)=?,10,215,303,... - M. F. Hasler, May 16 2009

Crossrefs

Cf. A160256, A160218.

Programs

Python

from sympy import gcd
def A151413(n):
    if n <= 2:
        return n
    else:
        l1, l2, m, b = 2, 1, 1, {1, 2}
        for j in range(3, 10**9):
            i = m
            while True:
                if not i in b:
                    if i == n:
                        return j
                    l1, l2, m = i, l1, l1//gcd(l1, i)
                    b.add(i)
                    break
                i += m
        return "search limit reached." # Chai Wah Wu, Dec 09 2014

Formula

A160218(n) = a(A000040(n)), conjectured. - M. F. Hasler, May 16 2009

Extensions

a(13)-a(18) from Robert Gerbicz and M. F. Hasler, May 16 2009