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A238949 Degree of divisor lattice D(n). 3
0, 1, 1, 2, 1, 2, 1, 2, 2, 2, 1, 3, 1, 2, 2, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 2, 2, 3, 1, 3, 1, 2, 2, 2, 2, 4, 1, 2, 2, 3, 1, 3, 1, 3, 3, 2, 1, 3, 2, 3, 2, 3, 1, 3, 2, 3, 2, 2, 1, 4, 1, 2, 3, 2, 2, 3, 1, 3, 2, 3, 1, 4, 1, 2, 3, 3, 2, 3, 1, 3, 2, 2, 1, 4, 2, 2, 2, 3, 1, 4, 2, 3, 2, 2, 2, 3, 1, 3, 3, 4, 1, 3, 1, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Sung-Hyuk Cha (terms 1..200) & Antti Karttunen, Table of n, a(n) for n = 1..10000

S.-H. Cha, E. G. DuCasse, and L. V. Quintas, Graph Invariants Based on the Divides Relation and Ordered by Prime Signatures, arXiv:1405.5283 [math.NT], 2014.

Index entries for sequences computed from exponents in factorization of n

FORMULA

a(n) = A001221(n) + A056170(n) as given in the Cha, DuCasse, Quintas reference. - Geoffrey Critzer, Mar 02 2015

Additive with a(p^e) = 1+A057427(e-1). - Antti Karttunen, Jul 23 2017

MATHEMATICA

Prepend[Table[Total[FactorInteger[n][[All, 2]] /. x_ /; x > 1 -> 2], {n, 2, 85}], 0] (* Geoffrey Critzer, Mar 02 2015 *)

PROG

(PARI) a(n) = {my(f = factor(n)); sum(i=1, #f~, 1 + (f[i, 2] > 1)); } \\ Michel Marcus, Mar 03 2015

(Scheme) (define (A238949 n) (if (= 1 n) 0 (+ 1 (A057427 (+ -1 (A067029 n))) (A238949 (A028234 n))))) ;; Antti Karttunen, Jul 23 2017

CROSSREFS

Cf. A001221, A056170, A057427.

Sequence in context: A128428 A056171 A333749 * A076755 A317751 A106490

Adjacent sequences:  A238946 A238947 A238948 * A238950 A238951 A238952

KEYWORD

nonn

AUTHOR

Sung-Hyuk Cha, Mar 07 2014

EXTENSIONS

More terms from Antti Karttunen, Jul 23 2017

STATUS

approved

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Last modified May 6 09:45 EDT 2021. Contains 343580 sequences. (Running on oeis4.)