A089754 Smallest prime ending (least significant side) in n if possible else beginning in n.

11, 2, 3, 41, 5, 61, 7, 83, 19, 101, 11, 127, 13, 149, 151, 163, 17, 181, 19, 2003, 421, 223, 23, 241, 251, 263, 127, 281, 29, 307, 31, 3203, 233, 347, 353, 367, 37, 383, 139, 401, 41, 421, 43, 443, 457, 461, 47, 487, 149, 503, 151, 521, 53, 541, 557, 563, 157, 587, 59, 601, 61, 6203, 163

Offset

1,1

Links

Table of n, a(n) for n=1..63.

Maple

read("transforms)"):
nleadzero := proc(n, dgs)
    local ndgs ;
    if n = 0 then
        ndgs := 0 ;
    else
        ndgs := ilog10(n)+1 ;
    end if;
    [op(convert(n, base, 10)), seq(0, i=1..dgs-ndgs)]
end proc:
digcatL2 := proc(L1, L2)
    digcatL([op(L1), op(L2)]) ;
end proc:
A089754 := proc(n)
    local prep, a, dgs ;
    if isprime(n) then
        n;
    elif modp(n, 2) = 0 or modp(n, 5) = 0 then
        ndgs := convert(n, base, 10) ;
        for dgs from 1 do
            for prep from 0 to 10^dgs-1 do
                a := digcatL2(ListTools[Reverse](ndgs), ListTools[Reverse](nleadzero(prep, dgs))) ;
                if isprime(a) then
                    return a;
                end if;
            end do:
        end do:
    else
        for prep from 1 do
            a := digcat2(prep, n) ;
            if isprime(a) then
                return a;
            end if;
        end do:
    end if;
end proc: # R. J. Mathar, Sep 18 2015

Crossrefs

Cf. A018800, A062584, A068164.

Sequence in context: A371885 A107698 A068164 * A110743 A077549 A089356

Adjacent sequences: A089751 A089752 A089753 * A089755 A089756 A089757

Keyword

base,easy,nonn

Author

Amarnath Murthy, Nov 22 2003

Extensions

Corrected by R. J. Mathar, Sep 18 2015

Status

approved