OFFSET
1,2
REFERENCES
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
W. Sierpiński, Elementary Theory of Numbers. Państ. Wydaw. Nauk., Warsaw, 1964, p. 165.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe)
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
W. Sierpiński, Elementary Theory of Numbers, Warszawa 1964.
R. G. Wilson, V, Letter to N. J. A. Sloane, Jul. 1992
MATHEMATICA
a = Table[ 0, {250} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 251, a[ [ s ] ]++ ], {n, 1, 250} ]; Select[ Range[ 250 ], a[ [ # ] ] == 1 & ]
PROG
(PARI) list(lim)=my(v=vectorsmall(lim\1), u=List(), s); for(k=1, #v, s=sigma(k); if(s<=#v, v[s]++)); for(k=1, #v, if(v[k]==1, listput(u, k))); Vec(u) \\ Charles R Greathouse IV, Jun 15 2015
CROSSREFS
KEYWORD
nonn
STATUS
approved