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 A037171 Numbers n such that phi(n) = pi(n), i.e., A000010(n) = A000720(n). 15
 2, 3, 4, 8, 10, 14, 20, 90 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS David W. Wilson and Jeffrey Shallit showed that 90 is the last term. Leo Moser proved in 1951 that these are the only terms, but he missed the term 10. - Amiram Eldar, May 15 2017 phi(n) >= pi(n) for n >= 61, and phi(n) > pi(n) for n > 90. - Jonathan Sondow, Dec 02 2017 REFERENCES P. Birch and D. Singmaster, An elementary number theory result, Math. Soc. Newsl., 12 (1984), 10-13. D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, p. 11. LINKS Leo Moser, On the equation ϕ(n) = π(n), Pi Mu Epsilon Journal. Vol. 1, No. 5 (1951), pp. 177-180. FORMULA A037228(a(n)) = 0. - Jonathan Sondow, Dec 02 2017 EXAMPLE phi(10)=4, pi(10)=4. a(1)=2 since k=2 is the lowest index for which A000720(n) = A000010(n), i.e., EulerPhi(n) = PrimePi(n). - M. F. Hasler, Mar 30 2007 MAPLE select(x->numtheory[phi](x)=numtheory[pi](x), [\$1..999]); # M. F. Hasler, Mar 30 2007 PROG (PARI:) for(n=1, 1e5, if(primepi(n)==eulerphi(n), print(n))) /* M. F. Hasler, Mar 30 2007 */ CROSSREFS Cf. A000010, A000720, A037228, A037230. Sequence in context: A328092 A242762 A005542 * A308811 A295296 A186417 Adjacent sequences:  A037168 A037169 A037170 * A037172 A037173 A037174 KEYWORD easy,nonn,fini,full AUTHOR STATUS approved

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Last modified February 18 04:48 EST 2020. Contains 332011 sequences. (Running on oeis4.)