A072194 Replace all prime factors p of n with n-p.

1, 0, 0, 4, 0, 12, 0, 216, 36, 40, 0, 900, 0, 84, 120, 38416, 0, 3600, 0, 4860, 252, 220, 0, 223608, 400, 312, 13824, 14196, 0, 18900, 0, 24300000, 660, 544, 840, 1258884, 0, 684, 936, 1920520, 0, 54600, 0, 58212, 70560, 1012, 0, 201485520, 1764, 97200

Offset

1,4

Comments

a(n)=0 iff n is prime.

Links

Paolo P. Lava, Table of n, a(n) for n = 1..10000

Example

a(18) = a(2*3*3) = (18-2)*(18-3)*(18-3) = 16*15*15 = 3600.

Mathematica

Join[{1}, Table[Times@@(n-#&/@Flatten[Table[#[[1]], #[[2]]]&/@FactorInteger[ n]]), {n, 2, 50}]] (* Harvey P. Dale, Dec 04 2018 *)

Prog

(PARI) a(n) = {my(f = factor(n)); for (k=1, #f~, f[k, 1] = n - f[k, 1]; ); factorback(f); } \\ Michel Marcus, Mar 22 2018

Crossrefs

Sequence in context: A167296 A147607 A174087 * A225952 A273795 A273858

Adjacent sequences: A072191 A072192 A072193 * A072195 A072196 A072197

Keyword

nonn

Author

Reinhard Zumkeller, Jul 02 2002

Status

approved