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 A087126 Primes of the form p^k - p^(k-1) + 1 for some prime p and integer k > 1. 3
 3, 5, 7, 17, 19, 43, 101, 157, 163, 257, 487, 1459, 2029, 4423, 6163, 14407, 19183, 22651, 23549, 26407, 37057, 39367, 62501, 65537, 77659, 113233, 121453, 143263, 208393, 292141, 342733, 375157, 412807, 527803, 564899, 590593, 697049, 843643 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is usually the case that, for prime p and k > 1, the first time the totient function phi(n) has value p^k - p^(k-1) is for n = p^k. However, this is not true when p^k - p^(k-1) + 1 is prime. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Eric Weisstein's World of Mathematics, Totient Function Eric Weisstein's World of Mathematics, Totient Valence Function MATHEMATICA lst={}; maxNum=10^6; n=1; While[p=Prime[n]; p^2-p+1

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Last modified September 25 19:42 EDT 2020. Contains 337344 sequences. (Running on oeis4.)