OFFSET
1,2
COMMENTS
The divisors are counted up to association.
LINKS
FORMULA
For prime p > 2, a(p) = 2^((p-1)/2) = sqrt(A005179(p)).
MATHEMATICA
a[n_] := If[n > 2 && PrimeQ[n], 2^((n-1)/2), Block[{k=1}, While[ DivisorSigma[0, k, GaussianIntegers -> True] != n, k++]; k]]; Array[a, 52] (* Giovanni Resta, Apr 04 2018 *)
PROG
(PARI) nbd(n) = {my(r=1, f=factor(n)); for(j=1, #f[, 1], my(p=f[j, 1], e=f[j, 2]); if(p==2, r*=(2*e+1)); if(p%4==1, r*=(e+1)^2); if(p%4==3, r*=(e+1)); ); return(r); } \\ A062327
a(n) = {my(k=1); while (nbd(k) != n, k++); k; } \\ Michel Marcus, Apr 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Jianing Song, Apr 04 2018
EXTENSIONS
More terms from Giovanni Resta, Apr 04 2018
STATUS
approved