This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
phi(34)=16, 33=3^1*11^1, 3+1+11+1=16.
Select[Range[20000],Total[Flatten[FactorInteger[#-1]]]==EulerPhi[#]&] (* Harvey P. Dale, Mar 27 2017 *)
phi(38)=18, 39=3^1*13^1, 3+1+13+1=18.
Select[Range[30000], EulerPhi[#] == Plus @@ Flatten@ FactorInteger[# + 1] &] (* Giovanni Resta, Jun 11 2016 *)
isok(n) = (f = factor(n+1)) && (sum(i=1, #f~, f[i,2]) + sum(i=1, #f~, f[i,1]) == eulerphi(n)); \\ Michel Marcus, Jun 03 2014
a(24) = a(2^3 * 3) = abs(2 - 3) + abs(3 - 1) = 3. a(27) = a(3^3) = 0.
a[n_] := Plus @@ (Abs[#[[1]] - #[[2]]] & /@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, May 04 2021 *)
a(n)=local(t); if(n<1, 0, t=factor(n); vecsum(abs(t[,1]-t[,2])))
For k = 54, its prime factorization is 2^1*3^3: 5+4 = 2+1+3+3 = 9. For k = 756, its prime factorization is 2^2*3^3*7^1: 7+5+6 = 2+2+3+3+7+1 = 18.
Select[Range[34000], DigitSum[#]==Total[Flatten[FactorInteger[#]]] &] (* Stefano Spezia, Sep 14 2024 *)
isok(k)={my(f=factor(k)); vecsum(f[,1]) + vecsum(f[,2]) == sumdigits(k)} \\ Andrew Howroyd, Sep 26 2024
from sympy.ntheory import factorint
c = 2
while c < 10000:
charsum = 0
for char in str(c):
charsum += int(char)
pf = factorint(c)
cand = 0
for p in pf.keys():
cand += p
cand += pf[p]
if charsum == cand:
print(c)
print(pf)
c += 1
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