A118256 Concatenation for i=1 to n of A005171(i); also A118255 in base 2.

1, 10, 100, 1001, 10010, 100101, 1001010, 10010101, 100101011, 1001010111, 10010101110, 100101011101, 1001010111010, 10010101110101, 100101011101011, 1001010111010111, 10010101110101110, 100101011101011101, 1001010111010111010, 10010101110101110101, 100101011101011101011

Offset

1,2

Links

Michael S. Branicky, Table of n, a(n) for n = 1..1000 (terms 1..30 from N. J. A. Sloane)

Formula

a(n) ~ 10^n * 0.10010101.... [Charles R Greathouse IV, Dec 27 2011]

Example

A005171 : 1,0,0,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,1 ................
a(1)=1, a(2)=10, a(3)=100, a(4)=1001, ...

Mathematica

Array[FromDigits@ Array[Boole[! PrimeQ@ #] &, #] &, 21] (* or *)
FromDigits@ IntegerDigits[#, 2] & /@ Last@ Transpose@ NestList[{#1 + 1, If[PrimeQ[#1 + 1], 2 #2, 2 #2 + 1]} & @@ # &, {1, 1}, 21] (* Michael De Vlieger, Nov 01 2016, latter after Harvey P. Dale at A118255 *)

Prog

(PARI) a(n) = sum(k=1, n, !isprime(k)*10^(n-k)); \\ Michel Marcus, Nov 01 2016
(Python)
from sympy import isprime
def a(n): return int("".join(str(1-isprime(i)) for i in range(1, n+1)))
print([a(n) for n in range(1, 22)]) # Michael S. Branicky, Jan 10 2022
(Python) # faster version for initial segment of sequence
from sympy import isprime
from itertools import count, islice
def agen(): # generator of terms
    an = 0
    for k in count(1):
        an = 10 * an + int(not isprime(k))
        yield an
print(list(islice(agen(), 21))) # Michael S. Branicky, Jan 10 2022

Crossrefs

Cf. A005171, A118255, A118257.

Sequence in context: A282954 A282984 A266071 * A351386 A102397 A132347

Adjacent sequences: A118253 A118254 A118255 * A118257 A118258 A118259

Keyword

nonn,base,easy

Author

Pierre CAMI, Apr 19 2006

Extensions

Corrected by Omar E. Pol, Nov 08 2007

Status

approved