A167781 a(n) = smallest number b such that b+n is the first number after b with phi(phi(b)) = phi(phi(b+n)).
1, 4, 45, 14, 58, 25, 68, 17, 183, 41, 27, 85, 274, 101, 875, 38, 184, 53, 478, 196, 848, 807, 23, 173, 615, 125, 271, 303, 189, 351, 405, 191, 1035, 667, 596, 218, 915, 133, 1525, 397, 376, 92, 1191, 449, 3466, 552, 47, 346, 404, 137
Offset: 1
Programs
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PARI
/* brute force search */ ppu(b)= { filename = "c:/math/ppu.txt"; if (!b,b=100000); v = listcreate(b+1); for(x=1,b,listput(v,eulerphi(eulerphi(x)))); z=b\5; sv = listcreate(z+1); for(y=1,z,listput(sv,0)); ct = 0; for(i=1,b, vi = 1; j= i + vi; noMatch = 1; /*print("Here is ",i," and ",v[i]);*/ while( (noMatch==1) && (vi < z) && (j < b), if (v[i]==v[j], if (sv[vi] == 0, /*print("*** Matching on ",vi," for ",i);*/ sv[vi] = i; ct+=1; ); noMatch = 0; , vi += 1; j += 1 ) ); if(nomatch==1,print(i," couldn't find a match before ",j)) ); for(i=1,z, if (sv[i]!=0, print(i,") ",sv[i]); write(filename,sv[i],",") , return(0)) ) }
Extensions
Edited by N. J. A. Sloane, Nov 12 2009
Comments