

A246850


Even numbers which cannot be represented by the surface area of an n1 X n2 X n3 block.


0



2, 4, 8, 12, 20, 36, 44, 60, 84, 116, 140, 156, 204, 260, 380, 420, 660, 924
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OFFSET

1,1


COMMENTS

Twice A025052, see there for further comments.


LINKS

Table of n, a(n) for n=1..18.


FORMULA

a(n) = 2 * A025052(n).
Surface area = 2*(n1*n2 + n1*n3 + n2*n3).


EXAMPLE

A 1 X 1 X 1 block has surface area 6. A 1 X 1 X 2 block has surface area 10. No n1 X n2 X n3 block of intermediate size exists, so there is no way to create an n1 X n2 X n3 block with surface area 8.


PROG

(Python)
from sympy import integer_nthroot
def aupto(lim):
e, r, lim2 = set(range(2, lim+1, 2)), set(), integer_nthroot(lim//2, 2)[0]
for n1 in range(1, lim2):
for n2 in range(n1, lim2):
for n3 in range(n2, lim+1):
r.add(2*(n1*n2 + n1*n3 + n2*n3))
return sorted(e  r)
print(aupto(1000)) # Michael S. Branicky, Feb 04 2021


CROSSREFS

Cf. A025052.
Sequence in context: A100684 A131770 A322419 * A294066 A163489 A095352
Adjacent sequences: A246847 A246848 A246849 * A246851 A246852 A246853


KEYWORD

nonn,fini


AUTHOR

Andreas Boe, Sep 05 2014


STATUS

approved



