Hiroshi Sekigawa Kenji Koyama Nonexistence conditions of a solution for the congruence x1<sup>k</sup> + ... + xs<sup>k</sup> = N (mod p<sup>n</sup>). 1283-1297 1999 68 Math. Comput. 227 db/journals/moc/moc68.html#SekigawaK99