12k+5=25p+20
12k=25p+15
k=(25p+15)/12∈N
k=(24p+12+p+3)/12=24p/12+12/12+(p+3)/12 =2p+1+(p+3)12∈N
p+3 |12, p+3 minim=12 , p minim=9., kmin=2p+1+1=18+1+1=20
k=20
p=9
Verificare
12*20+5=25*9+20
240+5=225+20
245=245 Adevarat, problemna este bine rezolvata
a=25p+20 unde p+3=12,24,36...12s
p=12s-3= {9,21,33,...}
a=25(12s-3)+20
a=300s-75+20
a=300s-45 ( se observa ca cel mai mic, 245 , verifica relatia)
300s-45<1000
a∈{245, 245+300, 245+600}= {245,545; 845}