OFFSET
1,1
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000 (first 6300 terms from Robert Israel)
EXAMPLE
tau(40) = number of divisors of 40 = 8; sigma(sum of prime factors of 40) = sigma(2 + 5) = 8. Hence 40 is a term of the sequence.
MAPLE
filter:= proc(n) uses numtheory;
tau(n) = sigma(convert(factorset(n), `+`))
end proc:
select(filter, [$1..10^4]); # Robert Israel, Jun 09 2020
MATHEMATICA
Select[Range[2, 10^4], DivisorSigma[1, Apply[Plus, Transpose[FactorInteger[ # ]][[1]]]] == DivisorSigma[0, # ] &]
PROG
(PARI) is(n) = my(f = factor(n)); numdiv(f) == sigma(vecsum(f[, 1])) \\ David A. Corneth, Jun 09 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Oct 15 2002
EXTENSIONS
Offset changed by Robert Israel, Jun 09 2020
STATUS
approved