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 A073175 First occurrence of an n-digit prime as a substring in the concatenation of the natural numbers 12345678910111213141516171819202122232425262728293031.... 4
 2, 23, 101, 4567, 67891, 789101, 4567891, 23456789, 728293031, 1234567891, 45678910111, 678910111213, 1222324252627, 12345678910111, 415161718192021, 3637383940414243, 12223242526272829, 910111213141516171 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This is to Champernowne's constant 0.12345678910111213... (Sloane's A033307) as A073062 is to A033308 Decimal expansion of Copeland-Erdos constant: concatenate primes. - Jonathan Vos Post, Aug 25 2008 LINKS Robert Israel, Table of n, a(n) for n = 1..999 Eric W. Weisstein, Champernowne Constant. [From Jonathan Vos Post, Aug 25 2008] Eric W. Weisstein, Copeland-Erdos Constant. [From Jonathan Vos Post, Aug 25 2008] EXAMPLE Take 1234567891011121314151617....; a(4)=4567 because the first 4-digit prime in the sequence is 4567. 1213 is < 4567 but occurs later in the string. a(5) = 67891 is the first occurrence of a five-digit substring that is a prime, 12345(67891)011121314... a(1) = 2 = prime(1). a(2) = 23 = prime(9). a(3) = 571 = prime(105). a(4) = 2357 = prime(350). a(5) = 11131 = prime(1349). - Jonathan Vos Post, Aug 25 2008 MAPLE N:= 1000: # to use the concatenation of 1 to N L:= NULL: for n from 1 to N do   L:= L, op(ListTools:-Reverse(convert(n, base, 10))) od: L:= [L]: nL:= nops(L); f:= proc(n) local k, B, x;   for k from 1 to nL-n+1 do     B:= L[k..k+n-1];     x:= add(B[i]*10^(n-i), i=1..n);     if isprime(x) then return x fi   od; false; end proc: seq(f(n), n=1..100); # Robert Israel, Aug 16 2018 MATHEMATICA p200=Flatten[IntegerDigits[Range[200]]]; Do[pn=Partition[p200, n, 1]; ln=Length[pn]; tab=Table[Sum[10^(n-k)*pn[[i, k]], {k, n}], {i, ln}]; Print[{n, Select[tab, PrimeQ][[1]]}], {n, 20}] PROG (PARI) {s=Vec(Str(c=1)); for(d=1, 30, for(j=1, 9e9, #s

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Last modified August 23 14:00 EDT 2019. Contains 326229 sequences. (Running on oeis4.)