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A039780
Numbers k such that phi(k) is equal to A008473(k-1).
1
5, 25, 1176, 1625, 7385, 18633, 21726, 30276, 32923, 36905, 46025, 50809, 55449, 60726, 89257, 102425, 151657, 185745, 278226, 289961, 301017, 319145, 373176, 394121, 459513, 779817, 815676, 827926, 1053019, 1055719, 1170153, 1399123, 1657865, 1663209, 1667326
OFFSET
1,1
EXAMPLE
phi(1176)=336, 1175=5^2*47^1, (5+2)*(47+1)=336.
PROG
(PARI) b(n) = my(f = factor(n)); for (k=1, #f~, f[k, 1] = f[k, 1] + f[k, 2]; f[k, 2] = 1; ); factorback(f); \\ A008473
isok(k) = (k>1) && (eulerphi(k) == b(k-1)); \\ Michel Marcus, Feb 25 2021
CROSSREFS
KEYWORD
nonn
EXTENSIONS
Title corrected and more terms from Sean A. Irvine, Feb 24 2021
STATUS
approved