

A063655


Smallest semiperimeter of integral rectangle with area n.


13



2, 3, 4, 4, 6, 5, 8, 6, 6, 7, 12, 7, 14, 9, 8, 8, 18, 9, 20, 9, 10, 13, 24, 10, 10, 15, 12, 11, 30, 11, 32, 12, 14, 19, 12, 12, 38, 21, 16, 13, 42, 13, 44, 15, 14, 25, 48, 14, 14, 15, 20, 17, 54, 15, 16, 15, 22, 31, 60, 16, 62, 33, 16, 16, 18, 17, 68, 21, 26
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OFFSET

1,1


COMMENTS

Similar to A027709, which is minimal perimeter of polyomino of n cells, or equivalently, minimal perimeter of rectangle of area at least n and with integer sides. Present sequence is minimal semiperimeter of rectangle with area exactly n and with integer sides.  Winston C. Yang (winston(AT)cs.wisc.edu), Feb 03 2002
Semiperimeter b+d, d >= b, of squarest (smallest db) integral rectangle with area bd = n. That is, b = largest divisor of n <= sqrt(n), d = smallest divisor of n >= sqrt(n). a(n) = n+1 iff n is noncomposite (1 or prime.)  Daniel Forgues, Nov 22 2009


LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = A033676(n) + A033677(n).


EXAMPLE

Since 15 = 1*15 = 3*5 and the 3*5 rectangle gives smallest semiperimeter 8, we have a(15)=8.


MAPLE

interface(quiet=true); for n from 1 to 100 do for i from floor(sqrt(n)) to 1 by 1 do j := floor(n / i); if (i * j = n) then printf("%d, ", i + j); break; end if; od; od; # from Winston C. Yang


MATHEMATICA

Table[d = Divisors[n]; len = Length[d]; If[OddQ[len], 2*Sqrt[n], d[[len/2]] + d[[1 + len/2]]], {n, 100}] (* T. D. Noe, Mar 06 2012 *)


CROSSREFS

Sequence in context: A158973 A071323 A071324 * A117248 A079788 A146288
Adjacent sequences: A063652 A063653 A063654 * A063656 A063657 A063658


KEYWORD

nonn


AUTHOR

Floor van Lamoen (fvlamoen(AT)hotmail.com), Jul 24 2001


EXTENSIONS

Corrected and extended by Larry Reeves (larryr(AT)acm.org) and Dean Hickerson, Jul 26 2001


STATUS

approved



