OFFSET
1,2
COMMENTS
From Robert Israel, Feb 20 2020: (Start)
a(n)=0 if n is divisible by 3, as the sum of three consecutive cubes is divisible by 3.
a(22) has 2132 digits, too large for a b-file: it is the concatenation of 99999999999999999999999999999998^3 to 100000000000000000000000000000019^3. (End)
LINKS
Robert Israel, Table of n, a(n) for n = 1..21
EXAMPLE
a(2)=827 because 827 is the smallest prime formed from concatenation of 2 consecutive cubes i.e. 8 and 27.
MAPLE
ccat:= proc(L)
local t, i;
t:= L[1];
for i from 2 to nops(L) do
t:= t*10^(ilog10(L[i])+1)+L[i]
od;
t
end proc:
f:= proc(n) local k, p;
if n mod 3 = 0 then return 0 fi;
for k from floor(n/2)*2+1 by 2 do
p:= ccat([seq((k-i)^3, i=n-1..0, -1)]);
if isprime(p) then return p fi
od
end proc:
f(1):= 0:
map(f, [$1..10]); # Robert Israel, Feb 20 2020
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Shyam Sunder Gupta, Apr 17 2005
STATUS
approved