A137179 - OEIS

A137179

a(n) = the smallest positive integer m such that d(m) + d(m+1) = n, where d(m) is the number of positive divisors of m. (a(n) is the smallest m where A092405(m) = n.)

1, 2, 3, 5, 8, 11, 15, 20, 24, 39, 35, 59, 80, 84, 195, 167, 120, 119, 224, 239, 399, 335, 440, 359, 360, 480, 1520, 539, 899, 719, 1224, 720, 840, 1079, 3135, 1259, 5183, 1260, 2400, 2160, 1680, 1679, 9408, 2880, 7056, 2639, 3024, 2520, 6240, 2519, 7055, 6929

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OFFSET

3,2

LINKS

Robert Israel, Table of n, a(n) for n = 3..250

MAPLE

N:= 100: # for a(3)..a(N)

V:= Array(3..N):

count:= 0: dp:= 1:

for m from 1 while count < N-2 do

d:= dp; dp:= numtheory:-tau(m+1);

v:= d+dp;

if v <= N and V[v] = 0 then

V[v]:= m;

count:= count+1;

od:

convert(V, list); # Robert Israel, Mar 31 2021

MATHEMATICA

a = {}; For[n = 3, n < 60, n++, i = 1; While[ ! DivisorSigma[0, i] + DivisorSigma[0, i + 1] == n, i++ ]; AppendTo[a, i]]; a (* Stefan Steinerberger, May 18 2008 *)

CROSSREFS

Cf. A092405.

Sequence in context: A131073 A062485 A175143 * A356549 A096777 A125811

Adjacent sequences: A137176 A137177 A137178 * A137180 A137181 A137182

KEYWORD

nonn

AUTHOR

Leroy Quet, May 11 2008

EXTENSIONS

More terms from Stefan Steinerberger, May 18 2008

STATUS

approved