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 A306510 Numbers k such that twice the number of divisors of k is equal to the number of divisors of the sum of digits of k. 1
 17, 19, 37, 53, 59, 71, 73, 107, 109, 127, 149, 163, 167, 181, 233, 239, 251, 257, 271, 293, 307, 347, 383, 419, 431, 433, 491, 499, 503, 509, 521, 523, 541, 563, 613, 617, 631, 653, 699, 701, 743, 761, 769, 787, 789, 811, 859, 877, 879, 941, 967 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From Robert Israel, Jul 28 2020: (Start) The first even term is a(2747)=68998. Includes primes p such that A007953(p) is in A030513. (End) LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA 2*A000005(k) = A000005(A007953(k)). EXAMPLE For k = 19, 2*A000005(19) = A000005(A007953(19)), 2*A000005(19) = A000005(10), thus k = 19 is a member of the sequence. MAPLE filter:= proc(n) 2*numtheory:-tau(n) = numtheory:-tau(convert(convert(n, base, 10), `+`)) end proc: select(filter, [\$1..1000]); # Robert Israel, Jul 28 2020 PROG (PARI) isok(k) = (k >= 1) && (2*numdiv(k) == numdiv(sumdigits(k, 10))); \\ Daniel Suteu, Feb 20 2019 CROSSREFS Cf. A000005, A007953, A030513, A306509. Sequence in context: A289355 A144214 A191043 * A129805 A289492 A262286 Adjacent sequences:  A306507 A306508 A306509 * A306511 A306512 A306513 KEYWORD nonn,base AUTHOR Ctibor O. Zizka, Feb 20 2019 STATUS approved

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Last modified July 28 08:44 EDT 2021. Contains 346321 sequences. (Running on oeis4.)