A254139 a(n) = smallest composite c for which there exist exactly n bases b with b < c such that b^(c-1) == 1 (mod c), i.e., smallest composite c which is a Fermat pseudoprime to exactly n bases less than c.
9, 28, 15, 66, 49, 232, 45, 190, 121, 276, 169, 1106
Offset: 1
Examples
With c = 49: there are exactly five bases b with b < 49 such that 49 is a Fermat pseudoprime, namely 18, 19, 30, 31 and 48. Since 49 is the smallest composite having exactly five such bases, a(5) = 49.
Programs
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PARI
for(n=1, 20, forcomposite(c=3, , b=2; i=0; while(b < c, if(Mod(b, c)^(c-1)==1, i++); b++); if(i==n, print1(c, ", "); break({1}))))
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