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A307481
Numbers that can be expressed as x+2y+z such that x, y, z, x+y, y+z, and x+2y+z are all positive squares.
1
625, 2500, 5625, 10000, 15625, 22500, 28561, 30625, 40000, 50625, 62500, 75625, 83521, 90000, 105625, 114244, 122500, 140625, 142129, 160000, 180625, 202500, 225625, 250000, 257049, 275625, 302500, 330625, 334084, 360000, 390625, 422500, 455625, 456976, 490000, 525625
OFFSET
1,1
COMMENTS
Generated by iterating through all combinations of x,y,z in the range 1..5000 (squared) and completing the addition pyramid (see Example section).
If k is in the sequence then so is k*m^2 for m >= 1. - David A. Corneth, May 04 2019
If a^2 + b^2 = c^2 then x = a^4, y = (ab)^2, z = b^4 gives a term x + 2y + z = c^4. - David A. Corneth, May 07 2019
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10575 (terms <= 3*10^10)
Sean A. Irvine, Java program (github)
EXAMPLE
Each addition pyramid is built up from three numbers x, y, and z as follows:
.
x+2y+z
/ \
/ \
x+y y+z
/ \ / \
/ \ / \
x y z
.
The first two terms, a(1)=625 and a(2)=2500, are the apex values for the first two pyramids consisting entirely of squares:
.
625 2500
/ \ / \
/ \ / \
225 400 900 1600
/ \ / \ / \ / \
/ \ / \ / \ / \
81 144 256 324 576 1024
PROG
(Magma) a:=[]; for sw in [1..725] do w:=sw^2; for su in [1..Isqrt(w div 2)] do u:=su^2; v:=w-u; if IsSquare(v) then for sx in [1..Isqrt(u)] do x:=sx^2; y:=u-x; if (y gt 0) and IsSquare(y) then z:=v-y; if IsSquare(z) then a[#a+1]:=w; break su; end if; end if; end for; end if; end for; end for; a; // Jon E. Schoenfield, May 07 2019
(C++) See Links section.
CROSSREFS
Cf. A000290 (squares).
Sequence in context: A043352 A223183 A171995 * A262798 A250431 A046755
KEYWORD
nonn
AUTHOR
Glen Gilchrist, Apr 10 2019
STATUS
approved