# [seqfan] Re: d(n) = d(n-1)*d(n-2) & d(n) = d(n+1)*d(n+2)

Maximilian Hasler maximilian.hasler at gmail.com
Fri Feb 12 21:14:45 CET 2010

```> 1) Those integers n, n>=3, such that d(n) = d(n-1)*d(n-2), where d(n) is the number of divisors of n.
>
> 3,24,..

(21:14) gp > for(i=1,10^5,if((o+0)*(o=d)==d=numdiv(i),print1(i",")))

3,24,120,150,195,216,294,312,399,440,459,525,540,558,570,615,630,663,693,696,744,759,774,858,999,1032,1095,1125,1152,1176,1239,1350,
1455,1470,1494,1608,1624,1659,1664,1710,1725,1734,1785,1860,1880,1896,1914,1920,2070,2079,2139,2142,2280,2295,2328,2343,2376,2424,2430,
2568,2574,2595,2616,2709,2712,2720,2730,2760,2790,2808,2919,2970,3003,3048,3135,3144,3192,3210,3219,3375,3456,3549,3560,3608,3630,3640,
3768,3795,3822,3834,3848,3870,3930,3933,3968,4020,4023,4074,4104,4179,4230,4340,4360,4365,4440,4452,4515,4518,4550,4584,4623,4653,4760,
4794,4875,4950,4995,4998,5060,5064,5080,5130,5160,5166,5208,5229,5235,5244,5320,5368,5382,5535,5610,5624,5655,5676,5688,5704,5820,5859,
5925,6024,6030,6072,6123,6135,6168,6279,6312,6420,6474,6504,6528,6555,6678,6688,6696,6744,6831,6858,6888,7035,7038,7059,
7084,7095,7140,7144,7150,7160,7208,7224,7296,7455,7479,7480,7530,7539,7656,7725,7770,7995,8008,8088,8103,8190,8200,8211,8235,8250,
8265,8319,8320,8355,8547,8670,8679,8680,8760,8778,8883,8888,8895,8925,8970,9015,9150,9210,9320,9435,9438,9460,9568,9624,9630,9672,9690,
9723,9735,9765,9804,9834,9867,9960,10062,10179,10314,10392,10476,10632,10664,10680,10725,10815,10824,10840,10875,10878,10959,10968,
10998,11055,11128,11240,11256,11430,11480,11679,11703,11704,11784,11790,11830,11865,12000,12015,12040,12078,12255,12360,12423,12435,
12438,12488,12495,12543,12570,12576,12705,12824,12831,12852,12855,12948,12954,13152,13224,13272,13293,13299,13368,13416,13452,13468,
13515,13560,13578,13635,13640,13656,13688,13692,13695,13734,13832,13875,13935,13992,14028,14140,14238,14250,14325,14391,14454,14472,
14535,14568,14586,14664,14670,14715,14739,14805,14920,14924,14931,14970,15060,15150,15232,15279,15363,15400,15428,15453,15498,15528,
15560,15672,15678,15720,15735,15816,15834,15855,15860,15870,15928,16000,16035,16107,16110,16280,16350,16359,16383,16419,16536,16554,
16608,16614,16635,16659,16680,16744,16764,16779,16824,16863,16872,16890,16974,16983,16995,17000,17004,17024,17034,17064,17184,17259,
17295,17352,17380,17384,17464,17523,17608,17625,17688,17736,17829,17864,17880,17925,17928,17934,17952,17955,18015,18018,18024,18054,
18084,18255,18330,18456,18483,18486,18495,18504,18522,18525,18555,18693,18696,18750,18879,18918,19032,19095,19110,19224,19290,19323,
19383,19422,19425,19448,19464,19479,19485,19544,19560,19575,19578,19815,19848,19880,19899,19964,19995,20040,20115,20136,20163,20223,

(21:14) gp > ##
***   last result computed in 109 ms.

```