A181362 a(n) is the starting position of the n-th occurrence of n in the string 123456789101112131415161718192021... .

1, 15, 37, 59, 81, 103, 125, 147, 169, 214, 235, 271, 307, 533, 836, 1139, 1442, 1745, 2048, 2651, 541, 708, 978, 1308, 1608, 1908, 2208, 2508, 2808, 4115, 2684, 3020, 3424, 3428, 4232, 4331, 4375, 4419, 4463, 6652, 3229, 4595, 4639, 4679, 4719, 4767

Offset

1,2

Links

Table of n, a(n) for n=1..46.

Project Euler, Problem 305: Reflexive Position

Prog

(Python)
def a(n):
    # a(n) is the starting position of the n-th occurrence of n in
    # the string 123456789101112131415161718192021    .
    full='~'+''.join(map(str, range(1, 10000)))
    def place(n, str_n, offset):
        p=full[offset:].find(str_n)+offset
        return p if n==1 else place(n-1, str_n, p+1)
    return place(n, str(n), 0)
# prints the first fifty terms
print(', '.join(str(a(i)) for i in range(1, 51)))

Crossrefs

Cf. A033307, A031297 (first occurrence).

Sequence in context: A118867 A260796 A296179 * A082112 A059605 A147221

Adjacent sequences: A181359 A181360 A181361 * A181363 A181364 A181365

Keyword

nonn,base

Author

Jon Palin (jon.palin(AT)gmail.com), Oct 15 2010

Status

approved