a(n) = Sum_{i=1..n} phi(i)*phi(i+1), where phi(n) = A000010(n) is Euler's totient function.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =23a(5) =35a(6) =59a(7) =83a(8) =107a(9) =147a(10) =187a(11) =235a(12) =307a(13) =355a(14) =419a(15) =547a(16) =643a(17) =751a(18) =895a(19) =991a(20) =1111a(21) =1331a(22) =1507a(23) =1667a(24) =1907a(25) =2123a(26) =2339a(27) =2675a(28) =2899a(29) =3139