A245229 Primes that are the sum of 7 cubes and no fewer.
7, 47, 61, 103, 113, 211, 223, 229, 311, 337, 401, 419, 491, 787, 1021, 1453, 1489, 1697, 2039, 3659, 4703, 5279
Offset: 1
Examples
a(1) = 7 = 1^3 + 1^3 + 1^3 + 1^3 + 1^3 + 1^3 + 1^3. a(2) = 47 = 3^3 + 2^3 + 2^3 + 1^3 + 1^3 + 1^3 + 1^3. a(3) = 61 = 3^3 + 2^3 + 2^3 + 2^3 + 2^3 + 1^3 + 1^3. a(4) = 103 = 4^3 + 3^3 + 2^3 + 1^3 + 1^3 + 1^3 + 1^3.
Programs
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Maple
for n from 1 to 10^4 do m:= floor(n^(1/3)); if m^3 = n then M[n]:= 1 else M[n]:= 1 + min(seq(M[n-j^3],j=1..m)); fi od: select(n -> M[n]=7 and isprime(n), [$1..10^4]); # Robert Israel, Jul 14 2014
Comments