A206286 Nonprime numbers starting with a digit 1.

1, 10, 12, 14, 15, 16, 18, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 128, 129, 130, 132, 133, 134, 135, 136, 138, 140, 141, 142, 143, 144, 145, 146, 147, 148, 150, 152, 153, 154, 155, 156, 158

Offset

1,2

Comments

Complement of A045707 with respect to A131835. Supersequence of A206288.

Links

Table of n, a(n) for n=1..54.

Mathematica

Select[Range[200], ! PrimeQ[#] && IntegerDigits[#][[1]] == 1 &] (* T. D. Noe, Feb 13 2012 *)

Prog

(Python)
from sympy import primepi
def A206286(n):
    def f(x): return n-1+x+((m:=10**(l:=len(str(x))-1))-(k:=min((m<<1)-1, x))-primepi(m-1)+primepi(k))-sum((m:=10**i)+primepi(m-1)-primepi((m<<1)-1) for i in range(l))
    m, k = n, f(n)
    while m != k: m, k = k, f(k)
    return m # Chai Wah Wu, Dec 10 2024

Crossrefs

Cf. A045707 (primes with first digit 1), A131835 (numbers starting with a digit 1).

Cf. A206288.

Sequence in context: A099103 A208271 A094879 * A116023 A062408 A127653

Adjacent sequences: A206283 A206284 A206285 * A206287 A206288 A206289

Keyword

nonn,base

Author

Jaroslav Krizek, Feb 12 2012

Status

approved