OFFSET
1,1
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..138 (all terms < 10^8)
EXAMPLE
sigma(reverse(352)) = sigma(253) = 288 = 234 + 54 = sigma(153) + sigma(53) = sigma(reverse(352-1)) + sigma(reverse(352-2)).
MATHEMATICA
rev[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Select[Range[3, 10^5], DivisorSigma[1, rev[ # ]] == DivisorSigma[1, rev[ # - 1]] + DivisorSigma[1, rev[ # - 2]] &]
PROG
(Python)
from itertools import count, islice
from sympy import divisor_sigma as sigma
def agen(): # generator of terms
dr2, dr1 = 1, 3
for k in count(3):
dr = sigma(int(str(k)[::-1]))
if dr == dr1 + dr2:
yield k
dr2, dr1 = dr1, dr
print(list(islice(agen(), 25))) # Michael S. Branicky, May 29 2024
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Joseph L. Pe, Apr 29 2002
EXTENSIONS
More terms from Sean A. Irvine, May 28 2024
STATUS
approved