login
A112015
Numbers n with odd length such that sigma(n) = (d_1^d_2)*(d_3^d_4) *...*(d_(k-2)^d_(k-1))*d_k where d_1 d_2 ... d_k is the decimal expansion of n.
2
1, 61845, 2165527, 3045365, 4461365, 109182857, 120068526, 132268815, 154514955, 166825505, 194565915, 194621658, 215365427, 216753138, 226262568, 228330759, 243430671, 243771445, 246455605, 276514536, 276751134, 277093299, 286551243, 287337804, 293644185
OFFSET
1,2
COMMENTS
The term a(7) = 120068526 makes use of the convention 0^0 = 1. - Giovanni Resta, Jun 06 2016
EXAMPLE
4461365 is in the sequence because sigma(4461365)=(4^4)*(6^1)*(3^6)*5.
MATHEMATICA
Do[h=IntegerDigits[n]; k=Length[h]; If[h[[k]] != 0 && OddQ[k] && Select[Range[k/2], h[[2#-1]] == 0 ==h[[2# ]] &] == {} && DivisorSigma[1, n] == h[[k]]*Product[h[[2j-1]]^h[[2j]], {j, k/2}], Print[n]], {n, 10^7}]
CROSSREFS
Sequence in context: A253613 A257749 A340126 * A234864 A128879 A234149
KEYWORD
base,nonn
AUTHOR
Farideh Firoozbakht, Sep 14 2005
EXTENSIONS
a(6)-a(25) from Giovanni Resta, Jun 06 2016
STATUS
approved