OFFSET
1,1
COMMENTS
Mainly primes. The first composite numbers in the sequence are 899, 102737, 194357, 217267, 377149, etc.
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..135 (terms < 10^10)
EXAMPLE
If n = 194357, starting from the least significant digit, let us cut the number into the set 7, 57, 357, 4357, 94357. We have:
sigma(7) - 7 = 1;
sigma(57) - 57 = 23;
sigma(357) - 357 = 219;
sigma(4357) - 4357 = 1;
sigma(94357) - 94357 = 759
and 1 + 23 + 219 + 1 + 759 = 1003 = sigma(194357) - 194357.
MAPLE
with(numtheory); P:=proc(q) local a, k, n;
for n from 2 to q do a:=0; k:=1; while (n mod 10^k)<n do
a:=a+sigma(n mod 10^k)-(n mod 10^k); k:=k+1; od;
if sigma(n)-n=a then print(n); fi; od; end: P(10^9);
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Apr 14 2014
STATUS
approved