OFFSET
1,1
COMMENTS
This is inspired by the self-locating digits in Pi (A057680). Similar to A064810, these digits are 0-indexed, whereas in A057680 the sequence is 1-indexed.
The first two terms of the 1-indexed sequence are 8031711 and 648967141. - Giovanni Resta, Apr 22 2020
EXAMPLE
37 is a term because the 3 digit of 37 appears in the 37th 0-indexed position of the Copeland-Erdős constant.
MATHEMATICA
q=23; p=3; dq=2; dn=dp=1; L={}; n=-1; pP=nP=10; While[++n < 10^6, If[n == nP, nP *= 10; dn++]; While[ q<n, p = NextPrime[p]; If[p > pP, pP *= 10; dp++]; q = q pP + p; dq += dp]; If[n == Floor[ q/10^(dq - dn)], Print@ AppendTo[L, n]]; q = Mod[q, 10^(--dq)]]; L (* Giovanni Resta, Apr 21 2020 *)
PROG
(Python)
import sympy
from sympy import sieve
def digits_at(ss, n):
''' Extracts len(str(n)) digits at position n.'''
t = len(str(n))
s = ss[n:n+t]
if s == '':
return -1
return int(s)
def self_locating(ss, n):
return digits_at(ss, n) == n
SS = ""
for p in sieve.primerange(2, 100000):
SS += str(p)
for i in range(100000):
if self_locating(SS, i):
print(i, end=", ")
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Soren Telfer, Apr 20 2020
EXTENSIONS
a(3)-a(13) from Giovanni Resta, Apr 22 2020
STATUS
approved