A332973 Solutions k of the equation usigma(k) = usigma(k-1) + usigma(k-2) where usigma(k) is the sum of unitary divisors of k (A034448).

3, 42, 188970, 998670, 51670374, 91397154, 236280786, 259172826, 792554574, 1106710914, 1468869930, 1957827498, 2467823442, 2496238590, 3324585210, 4055970282, 4183629690, 4384566870, 13479861630, 20681058270, 29343074178, 43449285210, 68705958690, 71418085926

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..64 (terms < 10^13)

Example

42 is a term since s(42) = 96 and s(40) + s(41) = 54 + 42 = 96.

Mathematica

usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); Select[Range[3, 10^8], usigma[#] == usigma[# - 1] + usigma[# - 2] &]

Prog

(PARI) usigma(k) = sumdivmult(k, d, if(gcd(d, k/d)==1, d)); \\ A034448
isok(k) = usigma(k) == usigma(k-1) + usigma(k-2); \\ Jinyuan Wang, Mar 08 2020

Crossrefs

The unitary version of A065900.

Cf. A034448, A065557, A075565, A076136, A145469, A291126, A291176, A292033, A294995, A332974.

Sequence in context: A058808 A155210 A157572 * A137192 A253577 A337213

Adjacent sequences: A332970 A332971 A332972 * A332974 A332975 A332976

Keyword

nonn

Author

Amiram Eldar, Mar 04 2020

Extensions

Terms a(22) and beyond from Giovanni Resta, Mar 10 2020

Status

approved