OFFSET
1,1
COMMENTS
Subset of A036537.
Old name was: Numbers with divisor number of form 2^k for some k which satisfying a special condition. - David A. Corneth, May 13 2018
LINKS
David A. Corneth, Table of n, a(n) for n = 1..14315 (terms <= 10^5).
FORMULA
Is a(n) ~ n/7? - David A. Corneth, May 13 2018
EXAMPLE
37 is in the sequence because the numbers of divisors of 37 through 43 are 2, 4, 4, 8, 2, 8, 2, which are all powers of 2. - David A. Corneth, May 13 2018
MATHEMATICA
SequencePosition[If[IntegerQ[#], 1, 0]&/@Log2[DivisorSigma[0, Range[3100]]], {1, 1, 1, 1, 1, 1, 1}][[All, 1]] (* Harvey P. Dale, Jan 17 2023 *)
PROG
(PARI) is(n) = my(res = 1); for(i=1, 7, if(factor(numdiv(n+i-1))[, 1]!=[2]~, return(0))); 1 \\ David A. Corneth, May 13 2018
(PARI) upto(n) = {my(res=List(), t=0); for(i=1, n+6, if(factor(numdiv(i))[, 1] == [2]~, t++; if(t==7, listput(res, i-6)), t=0)); res} \\ David A. Corneth, May 13 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Clarified, new name, corrected, extended and edited by David A. Corneth, May 13 2018
STATUS
approved