A215559 Smallest n-digit noncomposite number (written in base 2) with maximum base-2 digit sum.

1, 11, 111, 1011, 11111, 101111, 1111111, 10111111, 101111111, 1111011111, 11111110111, 110111111111, 1111111111111, 11101111111111, 100111111111111, 1111011111111111, 11111111111111111, 111011111111111111, 1111111111111111111, 10111111111111111111

Offset

1,2

Comments

In base 10: 1, 3, 7, 11, 31, 47, 127, 191, 383, 991,...

Links

Table of n, a(n) for n=1..20.

Maple

A215559 := proc(n)
    local ds, a, k;
    ds := 0 ;
    a := 0 ;
    for k from 2^(n-1) to 2^n-1 do
        if isprime(k) or k = 1 then
        if A000120(k) > ds then
            ds := A000120(k) ;
            a := A007088(k) ;
        end if;
        end if;
    end do:
    a ;
end proc: # R. J. Mathar, Aug 23 2012

Prog

(PARI) A215559(n)={my(p=2^n-1); !for(d=0, n-2, forvec(v=vector(d, k, [2, n]), isprime(p-sum(i=1, d, 2^(n-v[i])))|next; return(10^n\9-sum(i=1, d, 10^(n-v[i]))), 2))} \\ - M. F. Hasler, Aug 25 2012

Crossrefs

Cf. A004676, A069661.

Sequence in context: A267051 A101680 A267356 * A346231 A164553 A355280

Adjacent sequences: A215556 A215557 A215558 * A215560 A215561 A215562

Keyword

nonn,base

Author

Gerasimov Sergey, Aug 16 2012

Extensions

Corrected by R. J. Mathar, Aug 23 2012

Values double-checked by M. F. Hasler, Aug 25 2012

Status

approved