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A176707
Sum of digits of all distinct prime factors of n-th semiprime.
2
2, 5, 3, 7, 9, 8, 10, 4, 5, 6, 5, 10, 12, 12, 7, 7, 7, 11, 7, 13, 13, 6, 9, 8, 12, 9, 7, 13, 9, 14, 11, 7, 13, 15, 10, 13, 10, 16, 15, 2, 9, 8, 10, 17, 15, 14, 10, 6, 16, 12, 9, 18, 11, 12, 13, 4, 17, 19, 10, 15, 10, 18, 16, 4, 18, 10, 6, 12, 11, 10, 12, 11, 12, 13, 12, 7, 16, 19, 14, 14, 7
OFFSET
1,1
LINKS
EXAMPLE
a(1)=2 because 1st semiprime=2*2 and 2=2; a(2)=5 because 2nd semiprime=2*3 and 2<3.
MAPLE
A007953 := proc(n) add(d, d=convert(n, base, 10)) ; end proc:
A176707 := proc(n) s := A001358(n) ; add( A007953(p), p = numtheory[factorset](s) ) ; end proc: seq(A176707(n), n=1..120) ; # R. J. Mathar, Apr 25 2010
PROG
(Python)
from sympy import factorint
def aupton(terms):
alst, m = [], 4
while len(alst) < terms:
f = factorint(m)
if sum(f.values()) == 2: # semiprime
alst.append(sum(sum(map(int, str(p))) for p in f.keys()))
m += 1
return alst
print(aupton(81)) # Michael S. Branicky, Feb 05 2021
CROSSREFS
Cf. A095402.
Sequence in context: A191432 A135587 A191671 * A257533 A308021 A333201
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
a(13), a(34) etc. corrected by - R. J. Mathar, Apr 25 2010
STATUS
approved